Fix checks not running as expected after suspend

g_timeout-s use monotonic time, which doesn't get counted when the system is
suspended. As a result, the next automatic checks or the paused period would not
run when expected after a suspend.

We now use our own timeouts (via timerfd) using real time for next auto checks
and paused period.
Refactor escaping for notifications (Fix #3)

We now escape a few more characters, thus fixing a bug where notification-daemon
would not show the summary text if a '<' was used.
Escaping is only done on the fields where it applies (i.e. not for sizes, etc)
when send to notification (i.e. not for tty output), thus assuming that
user-provided templates are correctly escaped (to allow the use of tags, for
bold, etc).