Add possibility to use images as background or handle of slidevalue

* Add tag <resource background="x" handle="y" handlehover="z" />
  to the slidervalue object.
* All images are optional, e.g. you can use just handle or just
  background image or no images whatsoever

Change-Id: Ie0fee92965c6e883c4e532732756008dcc9e385e
Signed-off-by: Vojtech Bocek <vbocek@gmail.com>
remove stray test file
exfatfsck: ELF 64-bit LSB  executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=c91c3e4c1e542e4a40bcad47ac747f62fb7312f9, not stripped

Change-Id: I32472d460a8f03776e1d215810c537b029789220