fix thumbnail badge size

the old version gave

  TypeError: cannot concatenate 'str' and 'int' objects

when only one of thumbnail height and width was set on the
instance level.
Merge pull request #721 from xi/feature-fix-thumbnail-size

fix thumbnail badge size
Fix typo in instance.logo
Merge pull request #712 from xi/feature-refactor-logo

refactor logo
Add edit categories button / overlay to category page
remove unneeded code
don't recalculate locale strings all the time
i18n: extract new messages
Pull in English translations from en_GB in Transifex (fixes #102)

As Transifex doesn't allow to translate the source language, it wasn't
possible to translate English strings through Transifex, which lead to
an outdated English translation. We mostly avoided translating source
strings as this would break the other language's translations.

We originally planned to change the source language to something
artificial (e.g. en_AU), and use en as a proper translatable language.
However this would require deleting and readding the Adhocracy transifex
project entirely, as Transifex doesn't allow changing the source
language. As this would probably mean losing configution and maybe
collaborator, this is a nogo.

This commit fixes this issue in a much more simple way by forcing the
transifex client to also pull the en_GB translations, but store it in
the en folder.

[0] http://support.transifex.com/customer/portal/articles/1170853-can-i
-change-the-source-language-of-my-project-
i18n: Finally update en translation (see #102)

The English translation strings are rather incomplete currently, which
doesn't matter, as the source language (technical English) is always the
fallback language on a string level.

Therefore only English strings which vary from the source strings need
to be added in transifex.
i18n: update all translations
Add note about English translation in Transifex
Throw 404 instead of 500 for non-existing static page listing

Some backends don't have a static page index listing. As this route
isn't linked from anywhere using these backends, this now throws 404,
not a 500.
Show global permission table columns in deterministic order

Use Group.id as the order. Using the group name would be nicer, but
isn't more intuitive for admins which haven't set their language to
English, as the group name is translated.
Fix broken strings with double closing paranthesis
Add config option to disable email validation entirely

This can be useful in cases where no email can be sent.
Fixup: Use already existing config option required_email
Don't show attention getter if not require_email
mv locale to the top in instance settings
move display_category_pages to general settings