Merge remote-tracking branch 'origin/master' into retina
[NuGet] Allow double click to install package in Add Packages dialog.
[NuGet] Enter key now installs selected package in Add Packages dialog
[Icons] Removing obsolete icons:
* md-execution-marker (execution-marker-16.png)
* md-open-project-icon (open-project-16.png)
* system-file-manager (system-file-manager-16.png)
* md-visual-studio (visual-studio-16.png)
* (unreferenced) pin-gray-up-16.png
* (unreferenced) pin-green-down-16.png
* (unreferenced) pin-green-up-16.png
[Icons] New error, warning and done icons
[Icons] md-addins bump
Remove unused icons
Use our own icons for gtk-dialog-warning and error
[NuGet] Add infinite scrolling for packages in Add Packages dialog.
[NuGet] Fix duplicate packages in list view when scrolling.
Bump xwt
Updated reference to md-addins
[NuGet] Fix long package ids overlapping download count.
[NuGet] Improve display of package information in Add Packages dialog.

Add packages dialog right hand side package information improvements:

  Long package ids, authors now use ellipsis if they do not fit.
  Always show package version at top right hand side.
  Wrap package dependency list if the text is too long.
[NuGet] Allow long package names to be shown in Add Packages dialog.

Increase the size of the dialog so most of the packages with longer
names are visible in the list view.
[NuGet] Add more spacing to Add Packages dialog.

Add spacing to bottom edge of dialog.
Make buttons bigger.
Add spacing around package information in list view.
[NuGet] Format download count text using current culture.
[NuGet] Show different spinner label when searching for packages.
[NuGet] Support configuring package sources from Add Packages dialog.

Add 'Configure Sources...' option to NuGet feed combo box which when
selected closes the Add Packages dialog and opens the preferences
for package sources. Once the package sources have been updated the
Add Packages dialog is re-opened.

Move 'All Sources' to first in the feed combo box.
[Ide] Allow unified search categories to be extended by addins.

Add new extension path "/MonoDevelop/Ide/SearchCategories" so
an addin can make another search category available in the
main toolbar's unified search.