Add config "color" section to store colors
Rename config.setting.color_* to config.color.item_*

* Add a hook in tagger.py to handle this change
* Read config.setting.color_* values, store to config.color.item_*
* Delete old options
* bump picard version to 1.3.0dev1 to force config upgrade

It serves as a test case for the recently added config upgrade handling code.
Make tag status colors configurable (not yet through UI).
Add an optional description to options.
Add simple descriptions to tag_*_fg color options
Add generators to get list of options in a section

```python
# print keys for all options in config
for key in config.Option.keys():
   print key  # key = "section/name"

# print descriptions of all options in the color section
for i in config.color.keys():
   print config.color.get_description(i)
```
Add description to itemviews colors
ConfigSection: add method to retreive default value
Add option panel for configuring colors

For now, color changes may not be shown immediatly, it requires to alter code
because it was made for "constant" colors.
logview: make log colors configurable
Add "Changes here may not take effect until Picard is restarted." disclaimer.