Folder data sources (and other things)

This patch features a few new features:

• #172 Display a notification in case a plugin is used to display a log file
• #125 Introduce "Folder" data source
• #127 Titlebar shall contain more information
• #53 The font size should be configurable
• #66 Allow placement of bookmarks (bookmarks are finally persisted)

as well as one bug fix:

• #188 The proxy password box never looses focus

One plugin improvement:

• #189 Extend IFileFormatPlugin to allow regexp matching

Installer improvements:

• #150 Installer should stop Tailviewer
• #194 Installer doesn't display license anymore