Merge pull request #80 from special/fix-phone-comparison

[libcommhistory] Use localUid to determine when remote UIDs are phone numbers
[libcommhistory] Prevent numbers from comparing to empty after normalization

Phone numbers which return empty from normalization (e.g. no digits)
should not compare as equal unless the actual input is exactly equal.
[libcommhistory] Don't try to resolve contacts for empty UIDs
Merge pull request #81 from special/compare-uid-empty

[libcommhistory] Compare input phone numbers after normalization failure
[libcommhistory] Ignore contact accounts without localUid field for resolution

Valid accounts must have a localUid, and the empty field can be confused
with the syntax used for phone numbers, which leads to bad comparisons.
Merge pull request #82 from special/contact-empty-localuid

[libcommhistory] Ignore contact accounts without localUid field for resolution
WIP sketching out Recipient API
WIP Recipient implementation
WIP Begin porting Group to use Recipient
WIP