An attempt to do rigorous front-end input check.

Signed-off-by: Min Chen <minchnew@gmail.com>
Do rigorous front-end input validation on match fields.

Signed-off-by: Min Chen <minchnew@gmail.com>
No input validation on action target. Currently checking OUTPUT,
CONTROLLER and RESUBMIT.

Signed-off-by: Min Chen <minchnew@gmail.com>
Do front-end input validation while inserting a new flow.

While adding a new flow, match fields and actions are specified
separately. User inputs in the 'Match fields preview' textarea and
the 'Actions preview' textarea are checked against the Open vSwitch
flow syntax.

Signed-off-by: Min Chen <minchnew@gmail.com>
Merge branch 'flows-input-check'.

In the "Configuration/br-init/Flow Tables/New Flow Rule(s)" pop-up
window: flow specification can be very complicated and error-prone.
Do front-end input validation to make it easier for users to add a
new flow.

Signed-off-by: Min Chen <minchnew@gmail.com>