href-to should respect current state query parameters

[bekharsky]

Useful for combined filters. For example:

default route params:
tag: 'all',
from: '2016-04-07',
to: '2016-04-08',
fav: 'yes'

current state route params:
tag: 'vip',
from: '2016-04-01',
to: '2016-04-02',
fav: ''

How link-to works:

    {{link-to
      'prev'
      'games'
      (query-params from=ydEx to=ydTo)}}

result url: games?from=2016-04-06&to=2016-04-07&fav=&tag=vip

How equivalent href-to works:

<a href='{{href-to 'games' (query-params from=ydEx to=ydTo)}}'>prev</a>

result url: games?from=2016-04-06&to=2016-04-07&fav=yes&tag=all