[im] Update DirectoryRosterStore TODO note regarding Android API 26.
[im] DirectoryRosterStore.readEntry() should also catch IllegalArgumentException
[extensions] Add BoBDataExtension getBobData() and getContentId()
Those two methods where missing after the BoB API redesign.
Fix NPE in BoBIQ by adding XmlStringBuilder.optIntAttribute(String, Integer)
The method was missing and hence BoBIQ used optIntAttribute(String,
int) instead, which resulted in an NPE if the Integer was null.