mod_base: fixes a crash with is_a filter when input is rsc_alist and unknown cat
mod_admin: Add button to run schema install from the site's module again

This is a very handy button when changing the datamodel of a site
frequently while developing the site. It runs
SiteModule:manage_schema(install, Context) site callback function, to
install the site's default data.
core: Use lockfree os:timestamp() instead of erlang:now()
deps: new z_stdlib and new ua_classifier
core: fix error atom name for when ua_classifier can not load.
zotonic-tpl-mode: fix html tag highlighting when attr value contains //.
scripts: When zotonic is not running, echo the output of erl_call

This is to ease debugging situations where Zotonic in fact *is*
running but erl_call thinks it isn't.
mod_development: When activating a module, call Module:manage_schema(install, Context).

This makes development life easier while developing a module's schema.
mod_development: Remove unused function; shorten compilation notification
scripts: Fix typo in zotonic-update
mod_l10n: added translations for relative time desciptions in the core z_datetime.erl.
mod_base/core: added 'qarg' argument to postback actions.
Enables adding the value of input elements as query args to the postback.
mod_base: removed default error strings from validations. They are more often wrong than useful.
mod_base: moved the e-mail validation regexp to z_stdlib's z_email_utils.erl.
mod_authentication: fixes for password reset e-mail and some error feedback messages.
mod_admin_identity: added a control to add/verify e-mail identities instead of the e-mail address input for a person.
The verification is done by sending an e-mail with a verification link that needs to be followed.
Added extra maintenance functions to m_identity.
Added observer for #rsc_update_done{} to copy new e-mail addresses to the identity model.
deps: new ua_classifier lib
core: cache result of check if a specific module is enabled.
core: fix spec of function.
core: better error messages for z_db:q and q1 in case of sql errors.