Give every web view a separate user content manager
Add GSettings value for the default theme

This obsoletes the Astrognome.state.chart schema, which is removed.
Add enum <=> nick conversion functions

They are for planets, aspects and antiscia
Move used planets’ list to used_planets global array

This makes it easier to add new planets. A way should still be found to
automatically include related files in the default chart.
Update chart XSL

• Move planet group (<g>) creation to a template
• Add planet-X class to all aspect and antiscia lines so they can be hidden
  later one by one
• Move houses to their separate group
• Chart base is now a separate group, as it was intended
• Move from value_name to value_nick. It's shorter and makes using the
  substring function obsolete
• Antiscion lines got their own class
• Move away from visibility to display attribute. visibility in SVG can
  can be overridden, thus switching between aspects and antiscia cannot
  be done if the future display themes tamper with the lines’ visibility
  style
Refactor AgDb

Rename functions and type names so they are clearly related to charts.
This is required to implement display theme manipulation in the database.
Display theme implementation

It has only built in display themes yet.
Adding display theming possibility to the chart display
Move web view creation to its proper place (to ag_window_init())

This is necessary as ag_window_set_default_display_theme() would
indirectly manipulate the chart view’s theme, which fails (as the chart
view doesn’t exist at the time of manipulating).
Add some debugging instructions about display themes
Clean up AgPreferences template
Add default display theme selection to the Preferences
Merge pull request #77 from gergelypolonkai/display-themes

Add display theme support