Initial support for saving settings to config.ini

Supported settings:
* currency
* measurement_format
* temperature_format
* sound_quality
edge_scrolling and forced_software_buffering can now be edited ingame.

* edge_scrolling
* forced_software_buffering
New setting: always_show_gridlines.
New setting: landscape_smoothing
New setting: show_height_as_units
New setting: save_plugin_data
Merge branch 'config-save-ini' of https://github.com/atmaxinger/OpenRCT2 into atmaxinger-config-save-ini
fix warnings
Merge branch 'atmaxinger-config-save-ini'