Color tokens for pinned tabs, Git and charts (#211)

VS Code 1.50 [1] (September 2020) introduced new theme color tokens
pinned tabs, Git integration and charts [2].
The following token have been added to make it more conform with Nord's
style:

- `tab.lastPinnedBorder` - border on the right of the last pinned editor
  to separate from unpinned editors.
- `gitDecoration.stageDeletedResourceForeground` - foreground color for
  staged deletions git decorations.
- `gitDecoration.stageModifiedResourceForeground` - foreground color for
  staged modifications git decorations.
- Colors intended to be used by data visualization extensions:
  - `charts.red`
  - `charts.blue`
  - `charts.yellow`
  - `charts.orange`
  - `charts.green`
  - `charts.purple`
  - `charts.foreground`
  - `charts.lines `

[1]: https://code.visualstudio.com/updates/v1_50
[2]: https://code.visualstudio.com/updates/v1_50#_new-theme-colors

Co-authored-by: Sven Greb <development@svengreb.de>

Closes GH-202

themes/nord-color-theme.json

@@ -17,6 +17,14 @@
     "button.background": "#434c5e",
     "button.foreground": "#d8dee9",
     "button.hoverBackground": "#4c566a",
+    "charts.red": "#bf616a",
+    "charts.blue": "#81a1c1",
+    "charts.yellow": "#ebcb8b",
+    "charts.orange": "#d08770",
+    "charts.green": "#a3be8c",
+    "charts.purple": "#b48ead",
+    "charts.foreground": "#d8dee9",
+    "charts.lines": "#88c0d0",
     "debugConsole.infoForeground": "#88c0d0",
     "debugConsole.warningForeground": "#ebcb8b",
     "debugConsole.errorForeground": "#bf616a",
@@ -112,6 +120,8 @@
     "gitDecoration.ignoredResourceForeground": "#d8dee966",
     "gitDecoration.conflictingResourceForeground": "#5e81ac",
     "gitDecoration.submoduleResourceForeground": "#8fbcbb",
+    "gitDecoration.stageDeletedResourceForeground": "#bf616a",
+    "gitDecoration.stageModifiedResourceForeground": "#ebcb8b",
     "input.background": "#3b4252",
     "input.foreground": "#d8dee9",
     "input.placeholderForeground": "#d8dee999",
@@ -237,6 +247,7 @@
     "tab.unfocusedHoverBorder": "#88c0d000",
     "tab.activeBorderTop": "#88c0d000",
     "tab.unfocusedActiveBorderTop": "#88c0d000",
+    "tab.lastPinnedBorder": "#4c566a",
     "terminal.background": "#2e3440",
     "terminal.foreground": "#d8dee9",
     "terminal.ansiBlack": "#3b4252",