Add code to start gnome-keyring with proper env vars

Code comes from xfce4-session
Merge branch 'dev-gnome-keyring'
Add GTK3 support to gnome keyring module
Bump version to 1.7.0
session: support_autostart_delay
Merge pull request #36 from infirit/master

Remove some leftover files
Merge pull request #35 from NiceandGently/master

session: support_autostart_delay
Make upower optional

This commit is just an improved version of the pull request by Wolfgang Ulbrich
at https://github.com/mate-desktop/mate-session-manager/pull/38
making it working with both upower and systemd, and improving configure part
GTK3: fix compile warning 'gtk_target_table_new_from_list' differ in signedness [-Wpointer-sign]
GTK3: Fix compile warning by using gdk_error_trap_pop_ignored()
Merge pull request #39 from NiceandGently/dev-GTK3

GTK3: fix some compile warnings
Add  to ACLOCAL_AMFLAGS for user added flags