Fix crash on latest MacOS version.

[jpd236]

• Update wxWidgets to 3.1.5 to fix https://trac.wxwidgets.org/ticket/19100
• wxWidgets 3.1.5 drops support for MacOS < 10.10, so bump to that minimum
• Remove obsolete wxWidgets patch

[jpd236]

Gave this a cursory test on Windows and Mac and it seems to at least be basically functional, though there may be trickier bugs under the covers.

The Mac UI is a bit different now, particularly with the toolbar. It looks off to me - I think the icons are probably 2x the size they're supposed to be, and it's odd that they're level with the window title now as opposed to below it, but I'm guessing this is meant to match newer Mac style better?

[mrichards42]

Will take a look at this in combination with my wxlua3 branch. My attempts at this without upgrading wxLua all failed with

./lua/wxbind/src/wxcore_event.cpp:2808:33: error: no matching constructor for initialization of 'wxPaintEvent'
    wxPaintEvent* returns = new wxPaintEvent(id);

[jpd236]

Yep, this PR is against the wxlua3 branch rather than the master branch for the same reason.

[mrichards42]

So it is :)