Sort soldiers combobox

[myk002]

Adds a combobox to the bottom of the craft soldiers page to allow for sorting by various attributes.

forum discussion: http://openxcom.org/forum/index.php/topic,3644.msg45136.html#msg45136
and some here: http://openxcom.org/forum/index.php/topic,3080.msg44664.html#msg44664

Modified ComboBox logic so that the list popup can be configured to appear above the combobox button if there is not enough room on the screen below. Behavior of all existing combobox widgets is unchanged.

[MeridianOXC]

I see that this PR is not very active...
Could we at least merge the "don't lose scroll position when reordering" feature? It is only 2 lines of code... and such a big QoL improvement!

[MeridianOXC]

I have recently cherry-picked this into my build and I have to say this is a very nice piece of code.

I have a few comments though if someone decides to merge it to master:

1. The "drop up" combobox currently detects if it should drop up or down automatically. I changed this to a constructor parameter. It should be the developer/designer who decides. Also, prevents unwanted side effects... for example on the "New Battle" GUI. And also, as a nice bonus, State and ComboBox don't have to be friendly classes anymore.
2. I couldn't find the reason for "_toggled = false;" added line. I removed it from my build and everything still seems to work fine.
3. in the CraftSoldierState, all the initList() changes are obsolete; Warboy already implemented the functionality differently. Only on one place, the function needs to be called with original scroll position as parameter (at the end of sorting).
4. In the constructor I would change "_cbxSortBy->setSelected(-1);" to "_cbxSortBy->setSelected(0);" so that the content of the combobox is displayed from the beginning (not the end) when first opened.

Lastly, big thanks again to myk002, this is a real life saver (and time saver).

[MeridianOXC]

Also:
5. I have extracted the typedef, struct and macros into separate files (SoldierSortUtil.h/cpp) to reuse them on other similar GUIs; Note: extracting them in just .h file doesn't work, you need also .cpp file for implementation for some reason, so you'll need to write two macros (one for header, one for impl)

[MeridianOXC]

And:
6. when Options::anytimePsiTraining is turned on, psiSkill can actually have a negative value... so the getter for this attribute needs to be written manually (just like for psiStrength); if psiSkill > 0 return psiSkill else return 0;

[myk002]

@MeridianOXC I'll merge latest master and get rid of the conflicts, but could you submit a PR to my branch with your changes so I don't duplicate your effort?

[myk002]

I've implemented all of Meridian's (excellent) suggestions, and have tested the code thoroughly with current master. Is there anything the devs would like to see for this pull request before it is merged?