embedded bot: Return message id for send_message and send_reply.
embedded bot: Return message id for send_message and send_reply.

This change is made to comply with the corresponding views for
the API. The incrementor implementation in zulip_bots won't work
otherwise if send_message and send_reply return None as it needs
the message id.

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