The main UI components now use ScopedPointers for their children,
alleviating the need to call "deleteAllChildren" or "deleteAndZero"
in the destructor.

These should only be defined once. Instead of making them private to
ProcessorList, define them at global scope in ProcessorList.cpp, so
ProcessorListItem can use them too.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>

Three important changes:
- The FilterList is now the ProcessorList
- The FilterViewport is now the EditorViewport
- Any classes that need to access important UI objects have become subclasses
  of the "AccessClass". Such objects automatically obtain pointers from
  the UIComponent and register the MessageCenter as an ActionListener. This
  will make it much easier to allocate pointers to objects.

When an LfpDisplayCanvas was hidden for more than a few seconds, it would lose
track of the displayBufferIndex, causing it to pause for a few seconds when
it comes back into view. Now, the DataViewport sends a "refresh" reminder
to the canvas, to remind it to update its buffer indices in order to
display new data.

Tabs now work reasonably well when right-justified.

Border is now a square (except for upper-right corner).