Add methods to list and delete available messages

Deleting a "daily gift" message is necessary for later gifts to be received.
Rework base id from resource id calculation, use new constant

Correct first constant to subtract for FIFA 15 is 0x70000000 (1879048192)

Before:

 baseId(1879068993, True) -> (20801, 31)
 baseId(1929400641, True) -> (20801, 34)

After:

 baseId(1879068993, True) -> (20801, 1)
 baseId(1929400641, True) -> (20801, 2)
Merge pull request #91 from jamslater/master

Add methods to list and delete available messages, correct resource id calculation for FIFA 15