text correction and feature request for Optimizer tab

[zarl]

The current (as of 2017.0.0 beta) text for description and file selection in Optimizer tab says:

_ _ _
| Any variables below which are marked [x] will be optimized.\n
| Variables which are cleared [ ] will act as references or anchors.
|
| [ ] Only use control points between image selected in preview window.
_ _ _

First of all thanks a lot for the latest changes here. The earlier description is really improved. I only think we may need to differ between several terms when it comes to handling of the image files:

IMHO "cleared" doesn't fit here very well, it's better used if a queue needs to be cleared like in PTBatcherGUI.

 - marked / unmarked
   (this IMHO refers to the usage of checkboxes, correctly used in the dialog above)
 - selected / deselected
   (e.g. select one or more images from a list to process those via submenu command or by pressing a button)
 - activated / deactivated
   (I'd like to propose this term solely for what we have now available from the preview window where images can be disabled so they are not taken into account for display, move/drag, stitching etc.)

My proposal for a slightly altered text:

_ _ _
| Any variables below which are marked [x] will be optimized.\n
| Unmarked variables [ ] will act as references or anchors.
|
| [ ] Don't use control points of images deactivated in preview window.
_ _ _

Please note that I changed the last line from "only use" to "don't use" which doesn't change the logic of the checkbox but should better point out that deactivated images and their control points can be included or excluded from calculations.

And as an additional feature request: is it possible to point out to the user in this tab which images are deactivated in the fast preview window? Here are two possible solutions:
- displaying deactivated images with a greyed file name
- adding an additional column 'Active' located between '#' and 'Filename'

Further suggestion how to enable users to toggle activation without the need to switch over to the preview window:
- corresponding context menu command to toggle activation status
- cmd+click filename to toggle activation

[tmodes (tmodes)]

Fixed in default branch.
I also implemented the proposed feature.

PS: Interesting note, last time ctrl+click was too complicated, now you propose the same click by your own ;-)