Patches to port to webkit-gtk:4 and various other fixes (a lot for GTK3 port)

This patchset is roughly a result of the following in a wxWidgets repo clone
done on 2018-01-04:
git checkout -b 3.0.x origin/WX_3_0_BRANCH
git cherry-pick -x a309157a
git format-patch v3.0.3..

Followed by deletion of some patches that either add ABI or update version
number to 3.0.4.

This patchset is against 3.0.3, not 3.0.3.1, because otherwise the
docs/changes.txt changes inside patchset would conflict to a separate
changes.txt entry for 3.0.3.1 tag. This patchset includes the only change
included in 3.0.3.1 as well.


The patches that were ommited on purpose are as follows:

0002-Update-the-library-version-to-3.0.4.patch
0003-Also-update-build-bakefiles-version.bkl-for-3.0.4-an.patch
0080-Avoid-some-GTK-run-time-errors-when-using-wx-File-Di.patch
0085-Backport-GTKApplyCssStyle.patch
0086-Hide-wxSpinButton-s-underlying-GtkEntry-using-CSS-on.patch - relies on 0085
0096-Fix-ribbon-page-layout-wrong-when-scroll-button-is-s.patch

These patches are edited manually:
0004-Add-support-for-WebKit2GTK-in-wxWebView.patch - removed changes to setup0.h files (not present in release tarballs)
0013-Fix-monolithic-and-static-builds-after-WebKit2-suppo.patch - removed msw build file changes conflicting on newline type
0112-Move-wx-evtloopsrc.h-to-BASE_CMN_HDR-from-GUI_CMN_HD.patch - ^^^
