Lemur version 1.15.0

Incremental release with mostly bug fixes and javadocs. A few new convenience methods.

Change log:

• Fixed a bug where moving a GuiComponent from one GUI element to another
  caused lingering state issues. This most prominently manifested when
  using icons in ListBox labels.
• Added PopupState.clampToGui() for conveniently moving a GUI element so
  that it is fully on screen.
• Added additional convenience constructors to DocumentModelFilter that
  allow passing filters directly instead of setting them post-construction.
• Added PopupState.centerInGui() for conveniently centering a GUI element
  in the popup space.
• Added CommandMap.addCommands() and Button.addClickCommands() that take
  a single argument instead of var-args. This is the most common case
  and prevents a bunch of extra 'unchecked' warnings because of the
  var-args arrays.
• Fixed a subtle bug in the FocusManagerState where changing the focus
  during a focus change event may cause parts of the focus hierarchy
  to be left in an indeterminate state.
• FocusNavigationState.requestChangeFocus() now checks for null parameters
  and throws an IllegalArgumentException instead of an NPE further down
  in the stack.
• Added a TextField(model, elementId, style) constructor.
• Fixed TextEntryComponent to skip navigating focus if there is no current
  focus.
• Add some focusGained/focusLost trace logging to GuiControl.
• Added VersionedReference, VersionedObject, and VersionedHolder method
  javadocs.
• Fixed GuiControl.getPreferredSize() to return a clone of the preferred size
  override so that it's 'sharing' behvior matches that of when there is
  no preferred size override. (ie: you no longer have to defensively clone
  getPreferredSize() results even when there is an override in place.)
• Fixed an assertion error in PickEventSession.getPickRay() caused by 'bad'
  camera setups.