Enable "Add Source" button upon restart. [1074]

There appears to be some weirdness with properly restoring the
TLEChooser’s file selection…but I’ve been banging my head against this
one for too long.

Notes about the issue are in the comments of TLEChooser.setSelectedFile.
Utility methods for working with component trees.

[0]
[0] Dreamweaver updates synced from web server.