Initial implementation of ClaimCode.reservedFor.

This doesn't yet alter queries for available claim codes, e.g. the
getUnclaimedCodesTxt badge route. Nor does it implement email/webhook
callback when someone is issued a reserved claim code. It just
implements the notion of a reserved claim code in the badge/claim model,
along with a new Badge method, reserveAndEmail(), which creates a
reserved claim code, and changed the issueMany badge route to call it.
hooray for coppa
Added 'reserved for' column to claim code admin page.

Also added reservedFor property to claim objects in the
/v2/badge/<shortname>/claimcodes API call. (We might want to also allow
the client to filter out reserved claim codes if they want, though we're
not allowing for this now.)
renamed reserveAndEmail to reserveAndNotify.
profoundly confused by failing travis build, adding assertions to debug.
added imageUrl for issuer
Merge branch 'v2.0' of git://github.com/mozilla/openbadger into v2.0
Merge pull request #187 from curlee/v2.0

V2.0 adds imageurl to issuer
Fix some tests.
Remove badges from anonymous front page.
Exclude image data from responses.
Limit results
Move pagination buttons.
Always show previous button, disable when page == 1
Merge pull request #189 from mozilla/188-performance

Address performance issues on front page
Merge pull request #185 from toolness/reserved-claim-codes

[WIP] Initial implementation of ClaimCode.reservedFor.
Add simple search functionality.
Add a clear search button.
Remove misleading variable.
Only show badges when searching.