Update the list of supported select appearances

According to https://github.com/opendatakit/collect/blob/HEAD/collect_app/src/main/java/org/odk/collect/android/widgets/WidgetFactory.java#L222, we support
* compact
* minimal
* list-nolabel
* list
* label
* search / autocomplete
* image-map

Update the docs to reflect that. Might be good to update http://xlsform.org/en/ref-table/ as well.

Start by checking the supported appearance list in collect_app/src/main/java/org/odk/collect/android/widgets/WidgetFactory.java around line 222, then locate the corresponding select-appearance documentation. Update the docs to list all seven supported appearances and check whether the xlsform.org/en/ref-table/ reference should also be updated.

Written by the indexing model from the issue text.