Issues when deleting an existing layer

[aferrero2707]

When deleting an existing layer, the following issues are still present:

1. if opened, the right controls panel is not close/removed
2. similarly, the auxiliary control panel above the layers list is not removed
3. the image is not marked as modified
4. if the layer has a mask, and the corresponding layers tab is opened, the application crashes

The first three points need to be fixed before the next release. The fourth point is more complex to solve and will most likely be addressed in the next+1 release.

[aferrero2707]

Points 1, 2 and 4 are fixed in 0.2.0 release.

However, a crash still occurs when the deleted layer has either the sticky and/or the editing modes enabled.

[aferrero2707]

Everything should now be ok in the stable branch.
Related commits: 7e99c52 87d1b27 ad16291