translation generics added, more cleanups

Added generic terms for translation.
These are useful for buttons or actions or plugins that want to add a
bit of i18n to their plugin without the overhead of maintaining their
own translations I their plugin.
load cached pages into header 

to make available to backend pages
typo fix
cleaning up some functions

removed redundant code
Fix for authorization check bug on install

Added check for missing install.php, in case data files were wiped after
install avoid confusing 404 redirect.
fix for authorization.xml check fatal bug
fix #407 partial
added timeout control to curl fallback get_file_content
added configuration, api_timeout in ms.
defaulted and clamped to min 100ms if missing