zotonic_status: Add 'admin' button to sites overview

See here: http://stick.im/s/pNa
mod_admin: Add dropdown to set the number of items per page on the overview page

Fixes #703
docs: move tech design doc into its own directory.
mod_admin_identity: fix identity insert race condition by moving email identity check into the #rsc_update event instead of the async #rsc_update_done event.
core: let gettext show an error if a po file could not be read (instead of crashing)
core: emqtt, use the standard Erlang stdlib 'eacces' as error.
docs: fix example of lazy loader in combination with moreresults action
core/modules: changes to controllers for new webzmachine return values for provided charsets and encodings. See https://github.com/zotonic/webzmachine/issues/14
core: make sendfile behaviour switchable. Defaults to using the sendfile from Yaws.
See also http://erlang.org/pipermail/erlang-bugs/2013-October/003818.html
core: basesite skeleton: install mod_acl_adminonly before mod_authentication

Otherwise it won't work, because mod_authentication depends on an acl module.
mod_authentication: Reminder header should be translatable

Fixes #707.
mod_survey: in admin_frontend_edit, move question block to separate tabs.
mod_admin: fix mixed tabs/spaces (now spaces)
mod_base: simple fix capfirst on empty input. Still todo: make utf-8 safe.
mod_menu: allow 'none' to be returned from filter menu_rsc.
mod_survey: re-enable the forbidden check (was disabled for testing)
mod_survey: lazy initialization of tinymce editors in question tab.
mod_survey: add 'jump to question' functionality in the frontend-admin questions editor.
mod_survey: fix edit of page blocks. Fix sorter initialization of questions and jumps.
mod_survey: fix dragging tinymce blocks between question lists.