Removal of the 'default group' concept; removal of MC delete subscriber on remove from group

1. remove the MCAPI delete subscriber call from the remove-from-group
hook. This was causing data loss at Mailchimp - e.g. meaning Mailchimp
could not report how many people unsubscribed as the result of a
campaign, and possibly other bad things.

2. remove the default group concept because this would need to be on a
per-list basis to be useful.

3. require a grouping to be selected when mapping a group to a list.
This may require a "general" grouping or such. This is needed because if
we allow a group to link to a list without a grouping then add a
grouping at the MC end, then it's unclear whether the contact in Civi
should now be linked to the non-grouping group as well as the specified
grouping group.
WIP
added @todo comment
Implemented outline of code for new sync algorithm
Added euid, leid fields required for deletion/unsubscription into temp tables for new sync
merge fix83
towards suggested group setting UI
towards suggested group setting UI
Merge pull request #1 from deepak-srivastava/rich-master

suggested group settings UI - DB, quickform and js
fix server side validations
default options for a new group
Merge branch 'deepak-srivastava-rich-master'
schema changes at right place, and upgrade handler
Merge remote-tracking branch 'deepak/rich-master'
New sync from Civi to Mailchimp implemented. (some bits outstanding)
Added Mailchimp to Civi new sync code. Added some stats on a per list basis.
exclude opt outs, no emails, no bulk etc. etc.
Limit user to one group per list, or interest grouping
Implement user-selectable MC->Civi update limitation
webhooks fixed