feat: split nuxt-loading.vie in js/css files

feat: add css classes instead of style props

feat: add loader.css property

add nuxt-loading component tests with vue-server-renderer

revert flaky e2e progressbar test

add nuxt.options.loading.throttle option with defualt value 200

add pause/resume test

feat: new config option 'continuous'
If true the progress bar keeps changing also after duration time has
passed. It switches from ltr growing to rtl shrinking, then ltr growing
again with ltr: false

fix: remove Math.random() for percent increase, it caused choppy
behaviour and more importantly when loading took exactly duration time
there was a 100% chance the progress bar was not yet at 100%

fix: add safeguards so percent can never be <0 or >100

fix: calculate _cut correctly for duration < 1000

fix: remove automatically finishing when >95% is reached. This behaviour was
counter-intuitive, when duration time had almost passed duration the
progress bar always finished, regardless whether it was truly finished or
not. Now the progress bar stays at 100% until loading really finishes
(with continuous = false)

feat: add nuxt-progess-notransition class to disable transitions when we
are switching from grow to shrink

i just like to do things more difficult :s

fix: add yarn.lock after vue-jest install