Optimize item title retrieval

* Refine retrieval precedence
* Optimize: Gallery detection
* Close #15
Load admin client script only on settings page

* Add: new context entry for admin + `page` query value
* Update: Admin client script context
Load shadow files in client only when needed

* Client files can be defined to only load when other files are loaded that declare them as a dependency
Merge branch 'opt_client_admin' into develop
Limit loading of admin CSS to specific pages

Limit to settings page and plugin listing
Defer setting context until document has fully loaded