Stop capitalizing the proposal description entered by the user

This is broken, even for the default description (which is a date, where
"Tue" becomes "tue").
Improve suggested proposal name on creation so that it's unique

Until now, the default proposal name is "proposal" for all barclamps.
This is fine when the barclamp does not support multiple proposals, but
when it does, it means that the suggested proposal name might already be
in use.

Now we append a _1, _2, etc. string to the suggestion for the new
proposal name. That way, we guarantee that the user can directly create
the proposal.
Add ServiceObject.suggested_proposal_name to define suggested proposal names

This way, we allow barclamps to override
ServiceObject.suggested_proposal_name so that they will use "cluster_1"
instead of "proposal_1".
Merge pull request #988 from vuntz/better-proposal-name

Better proposal name