The old name was confusing, since the contents
of the div aren't just a table, and we have
smaller elements that actually do list a bunch
of subscriptions in tabular format.
We move templates related to listing streams in left pannel of
stream settings overlay to stream_settings folder by making
following changes:
* Rename `subscriptions.hbs` to `browse_streams_list.hbs`.
* Move `settings_stream_list.hbs` to stream_settings folder.
* Rename `subscription.hbs` to `browse_streams_list_item.hbs`.
* Move `settings_stream_list_item.hbs` to stream_settings folder.
We use subs as a common variable name for a collection of stream
data structure used in settings, in lot of modules. So this
rename clears a bunch of related shadowed variables.