Fix more incorrect USE_SPELLCHECKING checks.

Again. Freshly introduced by 179a4bfa.
Clear m_textTransPlural in DestroyContentView().

The rest of the code assumes that m_textTransPlural doesn't contain
nullptrs, yet DestroyContentView() kept the array and reset the pointers
in it.  This used to be fine when this function was only called from
PoeditFrame dtor, but no more.

Previously, this sequence of events could cause crash on Windows: open a
file, Ctrl+N, reopen the file.  Now m_textTransPlural would contain
twice as many entries, the first half of them nullptr.
Remove incorrect plural form DB entry for ar_SA.
Show both native and current locale lang names in UI lang picker.
Avoid potential double-destruction of FindFrame singleton.
Add Language::IsRTL() helper function.
Fix crashes related to closing the find window.

The use of wxWeakRef<> with incomplete class violated one definion rule,
possibly leading to memory corruption and other weirdness.  This is a
bug in wxWidgets that was fixed on the trunk, but not for 3.0.  See
http://trac.wxwidgets.org/ticket/15884

Fix by including full PoeditListCtrl definition.
Remove unneeded call to CatalogChanged().

This call is relatively expensive, so avoid it when not necessary.
RefreshControls() below does the same already.
Reset default invalid values of Team headers for new files.

Don't preserve the warnings-issuing, invalid value of Language-Team:
"LANGUAGE <LL@li.org>" for Language-Team.

Poedit used to always clear team metadata for new files.  That was too
much, so 625ce49ca790 removed that.  That was too little, the desirable
middle ground is to preserve meaningful entries, but clear the (invalid)
defaults.  The defaults are useless and only produce warnings that
pretty much nobody cares about these days.

See also 625ce49ca790
Update translations from Crowdin.
Increase version to 1.6.8, update NEWS.
OS X: Don't allow pasting formatted text into text controls.

Only paste as plain text, we don't preserve formatting.
Fix context menu assert with wxGTK 2.

Apparently, menu item must be appended before enabling/disabling it.
Fix possible wxEVT_TEXT infinite recursion under wxGTK.

See also 3b62a12f.
Fixes to editing RTL language files under LTR locales.

Properly align the text control as well as list entries when showing a
PO file that uses RTL (e.g. Arabic) when Poedit's UI language is English
or another LTR language.
Merge branch 'rtl-fixes' into stable
Auto-clear previous-msgid when clearing fuzzy flag.

When the user edits a string with fuzzy flag set and with previous msgid
(#|) entry, clear the previous msgid once the item is edited and the
fuzzy flag cleared.

Without this, Poedit would always keep the previous-msgid and would save
it even for non-fuzzy entries.  This was wrong.
Fix parsing of msgid="" w/ msgctxt.

Gettext header is the entry with the reserved msgid "", but _not_ if
msgctxt is non-empty - that's a different, unique entry. Correct
Poedit's parsing to check for the context.

Fixes #97.
Put /deps/* stuff together in .gitignore.
Set BiDi flags on win32 richedit control.

Set BOM_UNICODEBIDI and SES_BIDI flags when editing RTL text.