more dock options

changes from commit: 0a8941c6

• Renamed Appearance panel to Desktop (as this panel also consists of Dock-options)
• Renamed Window colors to Appearance
• Exposed more-options related to Ubuntu-dock as presented in issue: #2 (closed)
  • Added dock_extendheight_switch for the panel mode option.
  • Added dock_clickaction_combo with Default (focus-or-preview) and Minimze as items for the click action option.
  • Added dock_showmounted_switch for the Show mounted volumes and devices option.

screenshot: before

screenshot: after

Note: This MR should be merged after MR: Updates to Appearance Panel

Thanks