The Specifier component has some complex logic that allows users to modify the properties of a specifier in multiple ways, but this can lead to the specifier being overwritten just be opening it (#263). This PR sets about restructuring this component so that you can no longer modify the specifier just by opening it -- you have to explicitly modify something to trigger a modification action. (This is the minimum we need to close #263).

Now, we can't just remove all of this code, because the way in which Vue Store's data model works, we can't just plug the UI directly into the data object -- we have to call $store.commit('setSpecifierProps', {specifier, props}) or $store.commit('replaceTUnitForPhylogenyNode', {...}) to commit the results. So instead we need a model like this:

1. When the component is loaded, we load all of its values into a bunch of local variables, which model fields in the UI (so changing the UI immediately changes these fields). This is handled in the method loadSpecifier().
2. We watch all of these variables; if any of them change, we immediately update the underlying data object with the appropriate variables depending on the specifier type. This is handled in the method updateSpecifier().

Additionally, this PR:

• Removes Apomorphy as an option for the specifier dropdown (closes Remove "Apomorphy" from specifier type as we've now implementing it elsewhere #331).
• Changes the "Expand" button on the specifier to the clearer "Edit" (this still changes to "Collapse" when the editor is expanded).
• Fields that could previously be edited has now been made readonly.
• Renames the "Verbatim specifier" field to the clearer "Specifier label".

Closes #320: we don't include any special support for UUIDs, but we do now note that they can be used. They appear as collection IDs.

Example taxon:

Example specimen:

Example specimen with a UUID: