[webui] fix checkboxes being disabled when they haven't been
explicitly enabled
[webui] move the recording "Download" button to the toolbar
[webui] always reload the EPG store when the tab is activated

If we update the store when the tab is not activated the grid will be empty
once the tab is activated again. This fixes that plus fixes the issue where
the EPG data can be outdated if the web interface has been left open for a
long time and the active tab has been something other than the EPG tab.