Feature/mp suggestor

Add intelligence to MPTemplateSuggestor.

This patch makes MPTemplatesuggestor suggest VLANs and units dynamically, according to already used ones.

This patch creates VLANSuggestor and UnitSuggestor and makes MPTemplateSuggestor use them.
It also refactors SPTemplateSuggestor to use these two suggestors.

It has yet to be tested:
- SPTemplateSuggestor behaviour should not change.
- MPTemplateSuggestor should be able to suggest without fail.