unit test and refactor database.py

Updates to ``tests/framework/test_database.py`` and ``framework/database.py``.

- Replaced ``test_database.py`` ``unittest`` references with ``pytest`` references
- Removed test methods that checked the return type of database functions
- Added test methods that checked the return values of database functions
- Modified database functions to handle python strings properly
- Added bound values to the add_presentation and update_presentation database functions.
- Removed dummy record inserted by default.

Related gh484
I tried to reproduce it with the desktop record plugin and got a coredump with the following spit out:
```
2014-10-17 19:19:21,810 (   DEBUG) freeseer.frontend.qtcommon.FreeseerApp  : Detected user's locale as en_US
2014-10-17 19:19:21,873 (   DEBUG) freeseer.framework.plugin               : Plugin manager initialized.
2014-10-17 19:19:21,896 (   DEBUG) freeseer.framework.plugin               : Plugin manager initialized.
2014-10-17 19:19:21,896 (   DEBUG) freeseer.framework.multimedia           : Gstreamer initialized.
2014-10-17 19:19:21,906 (   DEBUG) freeseer.frontend.qtcommon.FreeseerApp  : Detected user's locale as en_US
2014-10-17 19:19:21,939 (   DEBUG) freeseer.framework.plugin               : Plugin manager initialized.
2014-10-17 19:19:21,939 (    INFO) freeseer.frontend.qtcommon.FreeseerApp  : Switching language to: English
2014-10-17 19:19:21,954 (   DEBUG) freeseer.frontend.qtcommon.FreeseerApp  : Detected user's locale as en_US
2014-10-17 19:19:21,963 (    INFO) freeseer.frontend.qtcommon.FreeseerApp  : Switching language to: English
2014-10-17 19:19:21,971 (    INFO) freeseer.frontend.record.record         : Loading settings...
2014-10-17 19:19:21,972 (    INFO) freeseer.frontend.qtcommon.FreeseerApp  : Switching language to: English
2014-10-17 19:19:27,287 (   DEBUG) freeseer.framework.multimedia           : Loading Output plugins...
2014-10-17 19:19:27,288 (   DEBUG) freeseer.framework.multimedia           : Loading Output: Video Preview
2014-10-17 19:19:27,313 (   DEBUG) freeseer.framework.multimedia           : Loading Video Recording plugins...
2014-10-17 19:19:27,313 (   DEBUG) freeseer.framework.multimedia           : Loading Video Mixer Input: Desktop Source-0
2014-10-17 19:19:27,332 (   DEBUG) freeseer.framework.multimedia           : Loading Video Mixer Input: Desktop Source-1
2014-10-17 19:19:27,484 (   DEBUG) freeseer.framework.multimedia           : Gstreamer paused.
2014-10-17 19:19:29,281 (   DEBUG) freeseer.framework.multimedia           : Recording started.
sys:1: Warning: cannot register existing type 'GstXImageSrcBuffer'

(__main__.py:13475): GLib-GObject-ERROR **: cannot create new instance of invalid (non-instantiatable) type '<invalid>'
Trace/breakpoint trap (core dumped)
```

I then relaunched freeseer with `python -m freeseer` in freeseer/src and click record -> stop -> prepare to record and get the following:
```
2014-10-17 19:22:38,859 (   DEBUG) freeseer.framework.multimedia           : Loading Output plugins...
2014-10-17 19:22:38,859 (   DEBUG) freeseer.framework.multimedia           : Loading Output: Video Preview
2014-10-17 19:22:38,882 (   DEBUG) freeseer.framework.multimedia           : Loading Video Recording plugins...
2014-10-17 19:22:38,882 (   DEBUG) freeseer.framework.multimedia           : Loading Video Mixer Input: Desktop Source-0
2014-10-17 19:22:38,893 (   DEBUG) freeseer.framework.multimedia           : Loading Video Mixer Input: Desktop Source-1

(__main__.py:13489): GStreamer-WARNING **: Name 'mainsrc_scale' is not unique in bin 'player', not adding
Traceback (most recent call last):
  File "freeseer/frontend/record/record.py", line 351, in standby
    if self.load_backend():
  File "freeseer/frontend/record/record.py", line 553, in load_backend
    initialized, self.recently_recorded_video = self.controller.load_backend(presentation)
  File "freeseer/frontend/record/RecordingController.py", line 58, in load_backend
    initialized, filename_for_frontend = self.media.load_backend(presentation)
  File "freeseer/framework/multimedia.py", line 273, in load_backend
    if not self.load_videomixer(videomixer, videomixer_inputs):
  File "freeseer/framework/multimedia.py", line 357, in load_videomixer
    mixer.load_inputs(self.player, self.videomixer, inputs)
  File "/home/kalen/Work/Repositories/freeseer/src/freeseer/plugins/videomixer/pip/__init__.py", line 123, in load_inputs
    map(lambda element: player.add(element), mainsrc_elements)
  File "/home/kalen/Work/Repositories/freeseer/src/freeseer/plugins/videomixer/pip/__init__.py", line 123, in <lambda>
    map(lambda element: player.add(element), mainsrc_elements)
gst.AddError: Could not add element 'mainsrc_scale'
```

It the configuration has picture-in-picture too so it looks related to #389 and #422