[WIP] Feature: Made TV Channels sidebar resizable and hence hideable

[lakshminarayananb]

Implementation for #44 :

• Changed the TV group channel side bar as gtk-paned instead of gtk-box container
• As gtk-box container already had only 2 child widgets inside - sidebar and playback_box, this is a straight swap to gtk-paned
• Added gtk-frame inside gtk-paned to place the sidebar and playback_box as it was recommended per the gtk doc
• Also, tidied up an existing behavior of the player showing an empty channels list when navigated from status bar 'Show' button. Now the side bar is hidden. This can be enhanced further by listing the channels from the group potentially later.

This is my first contribution to a GTK project and appreciate any feedback, issues. Thanks.

[mtwebster]

Hi, can you rebase this please? When #265 was merged it created a couple of conflicts (it was opened in January but merged after you opened yours, unfortunately).

Thanks