OTHER: Losen up clang build dep for travis a bit.
BUG(26): Avoid resetting equalizer on startup.

Previously we listed the config values without any
hint of if these were the initial values or not. Should
they be the initial values, then there's no need to perform
additional refreshes since all we will get all values anyway.
BUG(27): Add AppData description.
OTHER: Remove old Vala bug workaround.
OTHER: Fix shutdown crash.

Previously we listened to columns_changed event to track
what columns to show in the FilterView. I think the reason
for this was to keep dynamic_columns up to date with the
current column order. This however had a side effect of
GTK emitting this event during shutdown when destroying
the columns, and while doing so our updating of the model
caused a crash.

Instead we now set the new dynamic columns via the remove
event, and inspect the available columns directly when getting
the configuration to save (columns, and their order).
OTHER: Fix bug when editing columns.

The reference to FilterModel used in FilterEditor
was pointing to the instance that existed at the time
when the dialog was opened. When selecting a new column,
or deselecting an existing one, the store is replaced,
and thus the next action must refer to the new version.

The fix was to simply access the FilterView model member
directly from the FilterEditor event handler.