Replaced the split view in MainMenu.xib with a PLSplitViewController that manages its own split view.
File browser width is now fixed on window resize.

Implemented the splitView:resizeSubviewsWithOldSize: delegate method in PLSplitViewController. In this method, the tab view's frame is changed with the resizing window, while the file browser width remains fixed.
Improved split view and window size constraints.

The minimum window width is constrained in MainMenu.xib. Implemented the splitView:constrainMinCoordinate:ofSubviewAt: delegate method to constrain the file browser split view width.
Can no longer reduce tab view width to zero.

Added a constraint to the split view (the main window's content view) in conjunction with an implementation of splitView:constrainMaxCoordinate:ofSubviewAt: delegate method.
Removed layout constraint for main window and instead implemented the max split view width.

The constraint in LiasisAppDelegate.m was used to enforce a 2-fold width difference between the window's contentView and the tab view. Instead, this commit improves the implementation of splitView:constrainMinCoordinate:ofSubviewAt: delegate method in PLSplitViewController to enforce a similar behavior.
Added documentation to PLSplitViewController.
Set application window size in LiasisAppDelegate.m

In the awakeFromNib method, set the window's size and its minimum size. The minimum size was previously set in the xib file, but has now been removed.
Explicitly set the initial width of the file browser in the split view.
Automatically adjust the width of the file browser split view when decreasing the window size.

If the window size decreases such that the divider between file browser and tab view is greater than its minimum, automatically move the divider to the left as the window is resized. This required implementation of the splitViewDidResizeSubviews: delegate method in PLSplitViewController.
Added documentation for the PLSplitViewControllerMinimumViewMultiple constant and splitViewDidResizeSubviews: method.
PLSplitViewController is now initialized through a factory method.
Improved min/max file browser width determination.

PLSplitViewController now has properties to set the file browser's min/max relative (to the split view width) and absolute width.
Fixed an exception when auto-moving the divider.

Moved logic from splitViewDidResizeSubviews: for moving the divider on window resize into the splitView:resizeSubviewsWithOldSize: delegate method.
LiasisAppDelegate now specifies an absolute minimum file browser width for its splitViewController.
Fixed an issue where split view divider would jump when moving it after expanding window width.

Default minimumFileBrowserRelativeWidth is now set to zero. Therefore, the only minimum enforced is the absolute minimum specified by the LiasisAppDelegate. Without a relative minimum, the divider doesn't jump after increasing the window size.
Improved setting maximum file browser width.

The default maximumFileBrowserRelativeWidth is now 1.0 in PLSplitViewController. The LiasisAppDelegate sets it to 0.5.
Cleaned up applicationDidFinishLaunching: in LiasisAppDelegate.m
Cleaned up import statements in LiasisAppDelegate.
Added and improved the documentation in PLSplitViewController.
PLSplitViewController now allows for divider resizing in the positive direction.

This behavior is not utilized by the LiasisAppDelegate since the relative minimum width is set to 0.0.