Rework of #505

It is now apparent that page number validation cannot be done without
some participation from themes, at least themes that do "odd-ball"
things (such as having zenpage items on the index page.)

This change adds the ability for themes to participate in the decision
as to if page numbers are valid. Only default and perhaps zpmobile are
simple enough to not require participation.
Make URL page validation "opt-in" for themes

This is a change in behavior (all be it a good one) so theme designers
should not have to deal with it until at least 1.4.6
for now the URL page validation is a Debug Install option

There needs to be much more testing of this feature before it is
unleashed on the world. So it is now active only for themes that opt-in
and when the installation is a Debug Build. (Use the Mark release plugin
to set the build to debug.)

Also, Stopdesign, as a soon to be deprecated theme will not have support
added. (e.g. Stopdesign opts out!)
Fixes issues with news on index in Zenpage theme
Slovak translation update

update to the latest version.
fix typo
More on #505
Bad comment form link

Also some missing changes from the #505 sequence
fix #507
remove the html suffix from encrypted cachefile names
Explain #509 with a title hint
#496
Some minor issues with metatags
fix #511
fix #510
fix #509
Fix phantom "dot" album creation
prohibit instantiation of album named "."
Merge branch 'upstream/master'