Switch from vee-validate to vuelidate

[taoeffect]

Problem

• vee-validate injects errors into every component (although this can apparently be disabled via the config by setting inject to false)
• vee-validate has kinda an ugly API
• vee-validate is huge, the main .min file is 72.2kb, and the minimal version is still a whopping 33.3kb.

Solution

Look into other validation plugins.

Current promising candidate is vuelidate.

/cc @hubudibu

Update: Yep, looks like we're switching to vuelidate, so let's replace all of the vee-validate stuff with it.