subs: Trigger stream-creation UI for users permitted to create stream.
subs: Trigger stream-creation UI for users permitted to create stream.

The previous commit remove an obsolete form laying within
subscription_table_body.hbs. However, doing so broke the functionality
of triggering the stream-creation modal using the 'Enter' hotkey.

This commit re-introduces the functionality of loading the stream
creation modal only if the user has the permission to create streams.

At the same time, we make sure it's still possible to subscribe to
streams within zephyr mirroring organizations.

zulip/zulip,hackerkid/zulip,rht/zulip,hackerkid/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,rht/zulip,kou/zulip,andersk/zulip,punchagan/zulip,andersk/zulip,zulip/zulip,eeshangarg/zulip,hackerkid/zulip,kou/zulip,kou/zulip,rht/zulip,rht/zulip,kou/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,punchagan/zulip,andersk/zulip,andersk/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,kou/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,punchagan/zulip