Add enablers for evdev event mapping

MCE assumes that certain events have strongly defined meaning, but on
some devices kernel is emitting events that do not match expectations
that mce has about them.

Make it possible to add configuration files that are used to translate
events kernel is emitting into what makes logical sense to mce.

[mce] Add enablers for evdev event mapping
Make keypad slide policies work again

During tklock rewrite display blanking and autorelock policies based
on keypad slider state were broken.

Make keypad slide out/in work similarly as it used to with Nokia
N900 and N950 devices: Unblank display and hide lock screen when
keypad is slid out. If display was turned on due to keypad slide and
no touch input / calls are observed, blank display when the keypad
is slid in again.

[mce] Make keypad slide policies work again. Fixes JB#24391
Merge pull request #227 from spiiroin/jb24391_keypad_slide_policy

Make keypad slide policies work again
Bump mce version to 1.38.0
WIP add fixme notes
WIP turn off optimizations -> better valgrind call stacks
WIP Saturate DBusMessage caching in libdbus to help memory leak analysis

The libdbus keeps a cache DBusMessage objects and recycles them. While
this is good from performance point of view, it also means that some
messages are never released and are attributed in valgrind logs to the
place that happened to do the initial allocation. This makes it difficult
to see if messages are leaked or not.

By creating a number of dummy dbus messages and then releasing them
we can saturate the caching mechanism. After this we can be relatively
sure that DBusMessages are not being leaked as long all of them are
reported to originate from cache stuffing function.
WIP Add datapipe_execute_refcount_triggers() helper function

There are copy-pasted refcount_trigger loops scattered around
the datapipe module. These loops also use g_slist_nth_data()
effectively making O(N) task take O(N^2) time.

Replace inlined copy-paste loops with a call to helper function.
WIP Use single pass datapipe trigger iteration

Caveat: Will break if trigger does self-removal (or the next item)
WIP vebose datapipe init/quit