configure.ac: bump to version 1.7.0 for release
configure.ac: bump to version 1.7.0 for release

Gnurou/weston,sir-murray/weston,mchalupa/weston,kwm81/weston,mchalupa/weston,jonnylamb/weston,krezovic/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,udoprog/weston,eyolfson/weston,Fantu/compositor-spice,giucam/weston,krezovic/weston,xorgy/weston,giucam/weston,Tarnyko/weston-xdg_surface_present,eyolfson/weston,Gnurou/weston,udoprog/weston,jonnylamb/weston,xorgy/weston,sir-murray/weston,Fantu/compositor-spice,kwm81/weston