Support bgcolor of additional components

Maybe not needed that much, but mainly for consistency, to support
bgcolor in all dataclasses that represent boxes in the diagram.

docs/syntax.md

@@ -323,6 +323,7 @@ Parts can be added to a connector or cable in the section `<additional-component
   mpn: <str>           # manufacturer part number
   supplier: <str>      # supplier name  
   spn: <str>           # supplier part number
+  bgcolor: <color>     # Background color of entry in diagram component box
 ```
 
 Alternatively items can be added to just the BOM by putting them in the section `<bom-item>` above.

src/wireviz/DataClasses.py

@@ -114,6 +114,7 @@ class AdditionalComponent:
     qty: float = 1
     unit: Optional[str] = None
     qty_multiplier: Union[ConnectorMultiplier, CableMultiplier, None] = None
+    bgcolor: Optional[Color] = None
 
     @property
     def description(self) -> str:

src/wireviz/wv_bom.py

@@ -5,9 +5,9 @@
 from itertools import groupby
 from typing import Any, Dict, List, Optional, Tuple, Union
 
-from wireviz.DataClasses import AdditionalComponent, Connector, Cable
+from wireviz.DataClasses import AdditionalComponent, Cable, Color, Connector
 from wireviz.wv_colors import translate_color
-from wireviz.wv_gv_html import html_line_breaks
+from wireviz.wv_gv_html import html_bgcolor_attr, html_line_breaks
 from wireviz.wv_helper import clean_whitespace
 
 BOM_COLUMNS_ALWAYS = ('id', 'description', 'qty', 'unit', 'designators')
@@ -36,6 +36,7 @@ def get_additional_component_table(harness: "Harness", component: Union[Connecto
             common_args = {
                 'qty': part.qty * component.get_qty_multiplier(part.qty_multiplier),
                 'unit': part.unit,
+                'bgcolor': part.bgcolor,
             }
             if harness.options.mini_bom_mode:
                 id = get_bom_index(harness.bom(), bom_entry_key({**asdict(part), 'description': part.description}))
@@ -158,6 +159,7 @@ def component_table_entry(
         type: str,
         qty: Union[int, float],
         unit: Optional[str] = None,
+        bgcolor: Optional[Color] = None,
         pn: Optional[str] = None,
         manufacturer: Optional[str] = None,
         mpn: Optional[str] = None,
@@ -177,7 +179,7 @@ def component_table_entry(
               + (', '.join([pn for pn in part_number_list if pn])))
     # format the above output as left aligned text in a single visible cell
     # indent is set to two to match the indent in the generated html table
-    return f'''<table border="0" cellspacing="0" cellpadding="3" cellborder="1"><tr>
+    return f'''<table border="0" cellspacing="0" cellpadding="3" cellborder="1"{html_bgcolor_attr(bgcolor)}><tr>
    <td align="left" balign="left">{html_line_breaks(output)}</td>
   </tr></table>'''