Move panel view out into its own class

This is the first step in breaking out the commit view into tiny seperate view
objects to clean things up a bit.
Add title to panel view with custom navigation bar

The commit view shouldn't have to know about the title bar on a panel view so I
moved it over to that class.
Move scroll view into commit views init method
Add scroll view to each file view
Separate out the gutter view
Clean up view initializers
Pull out the line number labels into their own class
Move line labels out into their own class
Don't let the file view scroll view bounce
Better handle pulling down comments and their comments
Render subviews in file view initializer
Caclulate frame height after filling them
Rename gutter view to line number view
Rewrite view initializers with default parameters
Move all files into groups
Merge branch 'split-up-commit-view'