Zom Android 15.3 beta 6

f317906 update to build 1510031
37b826d more improvements for group membership work on #332 to confirm leaving group initial work on #344 to add crown to group admin
97f366c update build to 1510030
d1d782d improve file sharing, selection and import
50616f4 fixes for host, ip address and proxy support
f58a2f0 replace app name instances with Zom
6695d05 build 1510029
96f98cf more fixes for group membership and sharing
66442ae don't exclude existing contats, in case you need to reinvite them
4742294 truly fixes #335
609d3a5 improve display of media in message list
4d638c8 update translations
6484b2f update to build 1510028