Updated the keyboard routing document

Updated the keyboard routing document to describe the scenarios around
the peek definition window and the find UI.  There are a few bugs that
recently popped up in these components and we need to get more crisp
around what's happening here in order to correctly fix these bugs
Fix regression in handling of text editor key bindings

Restore correct filtering and ordering of fallback key bindings.

- Only TextEditor and Global bindings are applicable to to IWpfTextView instancees
- TextEditor bindings should be prioritized before Global bindings
Fix Shift+Left from last char of line
Merge pull request #1257 from ricksladkey/fixes-fallback-processor-regression

Fix regression in handling of text editor key bindings
Merge pull request #1256 from ricksladkey/fixes-1243-part-ii

Fixes #1243 - part II (select mode enhancements)
Cached the scroll and selection commands

The scroll and selection commands aren't dependent upon any document
state and hence can be cached.  Also took the oppurtunity to remove some
unused parameters from CommandFactory
Merge remote-tracking branch 'upstream/master'