Preserve the input when changing a dropdown

Currently, when choosing a new value in a drop-down, all values are blanked and reset to the default.

The goal of this ticket is to preserve the values of the parameters when they exist in the newly selected option.

For example, when switching from Equal to Not_Equal it should preserve the to value.

Values should only be preserved is the name matches - it is then within the realm of the API designer to control what is kept when switching from one constructor to another.