Currently there is a limit of 1000 users in the global
user list. This change introduces paging so that an
admin can see all users and not just the first 1000.

Adds a new route to the api - /api/users/search that
returns a list of users and a total count. It takes
two parameters perpage and page that enable paging.

Fixes #7469

Sorting datasources with case insensitive order

Sorts the list of metric sources that is used in dropdown for Panel
Data Source on the Metrics tab so that it is case insensitive and
so that the built data sources are last in the list.

The data source list is case sensitive when sorted. This changes the
sort to be case insensitive. The test only tests the handler, not the
routing or database query.

allow setting basic auth headers for prometheus datasource

* docs(plugins): new developing plugins section

Creates new section called Developing Plugins in
the plugin section of the docs.

1. Some changes to the Development guide page
2. Converted defaults/editor mode blog post
to new page
3. Converted snapshots blog post to new page
4. Adds new code styleguide page
5. Updates to apps and datasources pages
6. Adds plugin.json schema

* docs(links): fixes broken links

Fixes broken links to other pages as
well as broken image links.

* fix backendSrv request cancelling

* revert imports

* formatting

Fix typo