More replicator improvements

* Created a TD_DatabaseManager method to create replicators

Conflicts:
	Source/TDReplicatorManager.m
	Source/TD_DatabaseManager.m
Dumb bug fixes (TDReplication, TDBrowserIDAuthorizer)

Conflicts:
	Source/API/TDReplication.m
Change tracker needs to send cookies in its request

TDSocketChangeTracker uses CFHTTPMessageCreateRequest, which is too low-level to use the shared
cookie store, so it doesn't send any cookies. This breaks BrowserID auth, which is session-based.
Fixed this by explicitly getting the cookies from the NSHTTPCookieStore and adding their headers.
More BrowserID work (don't store assertion in database)

BrowserID assertions are extremely short-lived, so it doesn't make sense
to store them in a persistent replication's document. Instead, store the
email address only. The assertion is registered with the authorizer
before starting replication.

Conflicts:
	Source/API/TDReplication.h
	Source/API/TDReplication.m
	TouchDB.xcodeproj/project.pbxproj
Oops, I broke replication with that last commit

Fixes #219
BrowserID improvements

* Parse email address out of assertion rather than requiring it to be provided separately.
* Also get the expiration date, and don't return assertions that have expired.

Conflicts:
	Source/API/TDReplication.h
	Source/API/TDReplication.m
Fix a path-escaping bug with replication

Regression from the initial BrowserID patch (649d14f)