livereload task improvements

- use custom build command, with caching turned on - this reduces site
  build time by around 40% on my testing machines
- collect all glob patterns in a list and then call `server.watch`
  on each item - this allows to have single place where callback
  function must be specified
- use '**/*.html' as glob in template, to track changes in
  subdirectories

Pinning dependencies to specific versions creates conflicts when other
packages require more recent versions. We can do our part by allowing
for a wider range of dependency versions, specifying only the oldest
version that will still work. Meanwhile, we ensure that test
environments use a specific pinned dependency in order to match the
expected functional test output.

Class `lineno` was changed to `linenos`.