[Evolution] UI/Feature freeze break approval plea for 3.19.91

[Milan Crha <mcrha redhat com>]

        Hello,
I'd like to ask for a Feature Freeze break approval, together with a UI
Freeze break approval and, if accepted, I'd also announce a new strings
in the evolution, all for bug [761301], which adds an option to "Create
events, memos and tasks as Private by default" (that's also the added
string, once with a mnemonic, another time without it). The option can
be found in Edit->Preferences->Calendar and Tasks->General tab, in a
newly added section Miscellaneous, as the last section there.

It's pretty simple change in the code, and UI, but can improve
usability for users where privacy of this kind matters.

        Thanks and bye,
        Milan

[761301] https://bugzilla.gnome.org/show_bug.cgi?id=761301