webui: Use display name when displaying barclamp name as title

This makes the title consistent with the displayed name in the list of
barclamps.
Avoid browser password safe dialog in barclamp edit forms

For example, cinder backend password input tags trigger that but the
only password worth storing would be the crowbar admin password (if we
would use Rails instead of digest-auth).
Do not save node on allocate if already node is already allocated

This fixes an issue where the save call done for the allocation is
racing with the save call of a state transition for the same node.

It's not optimal for sure, though.
Allow reboot/shutdown on nodes without IPMI

We have code falling back to ssh commands when IPMI is not there.
Only show identify IPMI button for admin node

Obviously, poweron doesn't make sense. I don't think we want to allow
rebooting/shutting down the node this way, as there's a risk of the task
not completing and therefore breaking some internal consistency.
schema_migration: Fix off-by-1 error in downgrade
allow schema-migration to be missing

When it is missing, the rest of the code assumes a schema version
to be of 0. Otherwise we would need to add schema-migration 0
to all proposals, which requires a time machine.
schema_migration: fix case where schema-migration is missing in template
Merge pull request #686 from vuntz/allocate-once

Do not save node on allocate if already node is already allocated
Merge pull request #674 from vuntz/display-name-as-title

webui: Use display name when displaying barclamp name as title
Merge pull request #697 from vuntz/ipmi-buttons

Always show reboot/shutdown, except for admin node
Merge pull request #683 from saschpe/release/pebbles/master-form-autocompletion

Avoid browser password safe dialog in barclamp edit forms
Merge pull request #702 from vuntz/migration-fixes

Fixes in the schema migration code