remove warning when running `grunt dev`

This removes the warning 'path.existsSync is now called
fs.existsSync'. Now having one require at the top of the file,
as module.require caches requires anyway.
Fauxton: Improved pagination

This is an improvement and fix on the current pagination. This fixes
pagination so that it works with all query options.

Pagination in Couchdb is quite complex
and there are plenty of situations to cater for. This new pagination
works quite differently to the previous way we had it working for a
user.

A user can set the number of documents they want to view on a page. This
is not related to limit options in the query options - the limit option
is an overall cap of how many documents to paginate too. A limit of none
is possible and is the default. If the limit option is set to 50 and a
user wants 10 docs per page, the would then be able to paginate 3 pages
before hitting the end.

Another change is that the api url and browser url does not change when
we paginate. That happens internally and hence the new addition of
urlParams and docParams. This allows Fauxton to keep track of the
parameters that the user sees and the parameters that the document needs
to paginate.

Fixes COUCHDB-2067
Fauxton: Fix placeholder for Username

The one for Password has no `:` so removing them makes the view
more consistent (and looks maybe better)
Fauxton: Gruntfile fix more path.existsSync
Fauxton: Fix status messages in Active Tasks

Show Progress, current Sequence and Changes. Fix the display
of `undefined` if value is undefined.

Fixes #COUCHDB-2123