Be able to specify class field hints / descriptions when using ConfigurableClass

The current ConfigurableClass mechanism reads a field's pretty name and properly translates it.

However, if we want to add hints / descriptions to those fields, we can't really use the standard ConfigurableClass mechanism and we have to rewrite the entire form just for this.

The proposal is to look for translations of the following format: Space.ApplicationClass_fieldName.hint
If found, they should be displayed using the xHint xform class.

Note that some sections that are using an older XWiki.AdminFieldsDisplaySheet to customly display themselves are also applying the same logic.