Collapsing mode must not be turned off on removing gaps or undo

Use case 1:

1. Open a quite big alignment, e.g. ChikungunyaE1.fasta.
2. Turn on the collapsing mode.
   Expected state: the button is checked.
3. Press the Delete All Gaps button.
   Current state: the collapsing button is unchecked.
   Expected state: the collapsing mode stays turned on.

Use case 2:

1. Open COI.aln.
2. Turn on the collapsing mode.
   Expected state: two sequences are collapsed.
3. Edit the alignment.
4. Press Undo.
   Current state: the collapsing mode is OFF.
   Expected state: the collapsing mode stays turned on.