Add database macros for system, container, and component

Add the ability to use the PlantUML `database` shape for systems (including
external systems), containers, and components. The following macros have
been added:

- `SystemDb`
- `SystemDb_Ext`
- `ContainerDb`
- `ComponentDb`

These macros take the same parameters as their regular counterparts.

C4_Component.puml

@@ -22,6 +22,13 @@ skinparam rectangle<<component>> {
     BorderColor #78A8D8
 }
 
+skinparam database<<component>> {
+    StereotypeFontColor ELEMENT_FONT_COLOR
+    FontColor #000000
+    BackgroundColor COMPONENT_BG_COLOR
+    BorderColor #78A8D8
+}
+
 ' Layout
 ' ##################################
 
@@ -43,3 +50,6 @@ endlegend
 
 !define Component(e_alias, e_label, e_techn) rectangle "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//" <<component>> as e_alias
 !define Component(e_alias, e_label, e_techn, e_descr) rectangle "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//\n\n e_descr" <<component>> as e_alias
+
+!define ComponentDb(e_alias, e_label, e_techn) database "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//" <<component>> as e_alias
+!define ComponentDb(e_alias, e_label, e_techn, e_descr) database "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//\n\n e_descr" <<component>> as e_alias

C4_Container.puml

@@ -22,6 +22,13 @@ skinparam rectangle<<container>> {
     BorderColor #3C7FC0
 }
 
+skinparam database<<container>> {
+    StereotypeFontColor ELEMENT_FONT_COLOR
+    FontColor ELEMENT_FONT_COLOR
+    BackgroundColor CONTAINER_BG_COLOR
+    BorderColor #3C7FC0
+}
+
 ' Layout
 ' ##################################
 
@@ -43,6 +50,9 @@ endlegend
 !define Container(e_alias, e_label, e_techn) rectangle "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//" <<container>> as e_alias
 !define Container(e_alias, e_label, e_techn, e_descr) rectangle "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//\n\n e_descr" <<container>> as e_alias
 
+!define ContainerDb(e_alias, e_label, e_techn) database "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//" <<container>> as e_alias
+!define ContainerDb(e_alias, e_label, e_techn, e_descr) database "==e_label\n//<size:TECHN_FONT_SIZE>[e_techn]</size>//\n\n e_descr" <<container>> as e_alias
+
 ' Boundaries
 ' ##################################
 

C4_Context.puml

@@ -46,6 +46,20 @@ skinparam rectangle<<external_system>> {
     BorderColor #8A8A8A
 }
 
+skinparam database<<system>> {
+    StereotypeFontColor ELEMENT_FONT_COLOR
+    FontColor ELEMENT_FONT_COLOR
+    BackgroundColor SYSTEM_BG_COLOR
+    BorderColor #3C7FC0
+}
+
+skinparam database<<external_system>> {
+    StereotypeFontColor ELEMENT_FONT_COLOR
+    FontColor ELEMENT_FONT_COLOR
+    BackgroundColor EXTERNAL_SYSTEM_BG_COLOR
+    BorderColor #8A8A8A
+}
+
 ' Layout
 ' ##################################
 
@@ -75,6 +89,12 @@ endlegend
 !define System_Ext(e_alias, e_label) rectangle "==e_label" <<external_system>> as e_alias
 !define System_Ext(e_alias, e_label, e_descr) rectangle "==e_label\n\n e_descr" <<external_system>> as e_alias
 
+!define SystemDb(e_alias, e_label) database "==e_label" <<system>> as e_alias
+!define SystemDb(e_alias, e_label, e_descr) database "==e_label\n\n e_descr" <<system>> as e_alias
+
+!define SystemDb_Ext(e_alias, e_label) database "==e_label" <<external_system>> as e_alias
+!define SystemDb_Ext(e_alias, e_label, e_descr) database "==e_label\n\n e_descr" <<external_system>> as e_alias
+
 ' Boundaries
 ' ##################################