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.

GenericEditors now check their "selected" status before asking to be deleted.

The FilterViewport pauses for 50 ms after deleting a processor in order to
avoid double-deletions.

This reverts commit 307a5c3d.

Made UIComponent a MenuBarModel

Previously, if you placed a sink in front of a source, it would lead to
a never-ending "while" loop. By removing two lines (254-255), this problem
was solved.