add channel bulk controls + change default display of channels

[RFSH]

This PR,

• adds show/hide all, collapse/expand all
• changes the default behavior to only show the first 5 channels

I also removed the notion of opacity from channel.js and channel-item.js as it was not used at all. We're going to set the opacity to 0 or 1 depending on whether we want to show the channel or not.

56