Class based Context setting processors

For #11437
Implemented:
modContextSettingGetProcessor (not used in MODX)
modContextSettingRemoveProcessor
modContextSettingUpdateProcessor
modContextSettingUpdateFromGridProcessor

Renamed:
modContextSettingsGetListProcessor to modContextSettingGetListProcessor
modContextSettingsCreateProcessor to modContextSettingCreateProcessor

Fixed modx.grid.context.settings.js as in #12099 and to make use updatefromgrid processor