[webui] a bunch of improvements to the recordings section

Fixes:

* when a recording switches from "currently recording" to "finished", the "Upcoming recordings" window is now properly updated (the entry disappears) and "Finished recordings" is updated accordingly
* when a recording changes state (e.g. if it's deleted) and it's visible in the EPG filter, the state icon will now be updated accordingly

Improvements:

* the recording details dialog is now opened by pressing an Info icon instead of clicking the row itself
* multiple recordings can now be selected
* the "Add entry" button is now only visible in "Upcoming recordings" since it makes no sense in the other panels. In addition to this, a new button "Abort/unschedule" button is now available.
* a "Delete selected" button is available on the other panels which (wait for it...) deletes the selected recordings
* the Abort/Delete buttons that were previously in the Info details dialog have been removed

Various/dubios:

* removes duplicate check from the general "delete selected" function in tablemgr.js. The button is greyed out unless a selection has been made. I can drop this if you want.

@perexg @adamsutton for review (only tested in Firefox)
@mpmc for testing

Someone with stronger JavaScript-fu will have to refactor some of this crap some day so we can re-use the code a bit more.