Updated guide added

Updated channel management guide added
excessive images removed
changed following Dima's comments

Final version, hopefully
Update channel_guide.rst
Update channel_guide.rst
Update channel_guide.rst
Removed multichannel part
Update channel_guide.rst
Update channel_guide.rst
Update channel_guide.rst
Update channel_guide.rst
channels_entity_delete image added
minor update
minor update
channels grid picture changed
channel view picture and description changed
Update channel_guide.rst
Update channel_guide.rst
edit entities picture changed
delete entity picture changed