reorganize or merge settings and ui settings

After #49 UI settings are displayed in collapse elements, for the moment in two different ones. We should come up with a good way of splitting the properties between general/common and field-specific ones. The reorganization requires splitting properties between `ui:options` and `ui:` so rjsf's `getUiOptions` will be very useful for this as it returns all UI options no matter in which of the two ways they are specified. This task will require some small refactoring of some fields and widgets in order to accommodate this.

An **option worth considering** is merging both schema and uiSchema in one single schema (probably keeping the distinction in fieldTypes and merging after) and passing it to the settings form. Then in the settings we can arrange them however we want. E.g. discrete mode in slider and options and labels (otherwise options and labels would be in different tabs if we follow the correct rjsf way)