Use @RequestParam for page and pagesize parameters in Layers API list

Also removed a number of ApiController functions that were no longer used due to this change.

Note: This is a branch of https://github.com/boundlessgeo/suite/pull/703. Since they both modify similar regions of the same functions, I was hoping this will make merging easier(?). Consequently, https://github.com/boundlessgeo/suite/pull/703 should be merged first (or not at all).