We had two ways to generate an activity entry from a notice; one through
Notice::asAtomEntry() and one through Notice::asActivity() and
Activity::asString(). The code paths had already diverged somewhat. I
took the conditions that were in Notice::asAtomEntry() and made sure
they were replicated in the other two functions. Then, I rewrote
Notice::asAtomEntry() to use the other two functions instead.
This change passes the ActivityGenerationTests unit tests, but there
may be some other stuff that's not getting covered.
Moved the various classes used by the Activity class to their own
files. There were >10 classes in the same file, with around 1500 lines
in the file. Just too big.
This change makes autoloading work for these classes, so also removed
the hard require in lib/common.php.
