Create accurate filter for matching on from address (SMACK-71)

Smack contains two PacketFilters to filter on the from address.
FromContainsFilter simply does a substring match, which is problematic
as explained in SMACK-71. FromMatchesFilter partially fixes this
weakness, but it still uses String#startsWith to filter on bare
addresses. For example, when setup to match all JIDs with bare JID
"foo@example.co", it will still match "foo@example.com".

This commit changes FromMatchesFilter to test equality with the bare
from instead of startsWith with the full from.

Moreover, we convert all uses of FromContainsFilter to FromMatchesFilter
and remove FromContainsFilter. Additionally, the unused ToContainsFilter
(which as the same weaknesses) is removed, too.