Adds more navigation, view support

Re-added support for back/forward (not tab-specific, though, yet), and Up Level and Refresh. Also re-added support for the view items and zoom slider on the status bar. Added Content View and Thumbstrip View to the View tab. Also did a lot of reorganizing/categorizing of code.
Merge branch 'BetterExplorer2.5' of https://github.com/DimitarCC/BetterExplorer.git