Show commands rather than file set

Adds showQuickRepoHistory command to CodeLens
Adds showQuickCommitDetails command to the status bar
Adds showQuickRepoHistory command to the status bar
Changes recent CodeLens default command to showQuickCommitDetails
Changes status bar default command to showQuickCommitDetails

So that it can hide/restore the hover blame annotation if needed

Adds show changed files to commit quickpick
Changes ordering of commit quickpick list

It now opens commit details directly

Adds diffWithWorking to editor context menu
Renames diffWithPrevious for better clarity with new behavior
Renames diffWithWorking, diffLineWithPrevious, & diffLineWithWorking for better clarity

Consolidated lots of duplicate functionality
go back navigation should be robust now

Adds file history choices to commit quickpick
Adds repo history choice to file history quickpick
Adds commit message to quickpick placeholder in a few places

Moves show all quickpick item to be first

Tried to find the most recent filename given a commit, but git doesn't seem to want to cooperate

Wouldn't always grab the correct commit

Fixes #24

Adds blame toggle to the editor toolbar

Rearranges menu structure

Fixes #29 - Commit info tooltip duplicated for current line when blame is enabled
Improves performance of navigating line when active line annotations & statusbar blame are enabled

https://github.com/eamodio/vscode-gitlens/issues/26