Add support for multiple Vuetify versions

[dchiquito]

There is demand for this utility in different versions of Vuetify. Different Vuetify version have different elements. For example, 1.5 has v-list-tiles while 2.3 has v-list-items. Differentiating and testing these is challenging.

To start with, we only need to support 1.5 and 2.3 (currently the latest stable). I propose keeping a single package with different files exported for different versions. Instead of exporting vuetify-xpaths.js, we export vuetify-xpaths-1.5 and vuetify-xpaths-2.3.
Initially I think it's OK for these files to be copy/pasted. Once we have a grasp of the scale of the differences, maybe we can figure out a scheme to define all the methods in the base version (1.5) and have subsequent version apply some diff mutation to that base to minimize duplicate code. It's entirely possible that the differences are too substantial to merit this.

Testing is also difficult. We would need a new test app for each supported version, since each app can only have one version of Vuetify as a dependency. We should start with a copy/paste and similarly see if we can arrange some kind of dependency+diff chain to avoid supporting the same app multiple times.

All of this requires that we have reasonably complete support for a single version. Copy/pasting to a separate version will be much, much harder to maintain if we are still trying to add new methods, potentially across versions.