Fixing App unit test on Windows

- switched test from exact string to regex to match both types of paths
Replace underscore with lodash.
Merge pull request #1536 from jdalton/lodash
Removed mailto auto-linking.

fixes #1617
- Removed test
- Removed auto-linking from showdown gfm extension
We’re not really in alpha any more
Merge pull request #2132 from halfdan/1617-remove-mailto

Removed mailto auto-linking.
Resolve race condition which allows multiple users to be added

closes issue #1834
- Added an integration test which attempts to add multiple users asynchronously.
- Added closure to User.add()  which holds a state variable to determine if a user has been added.
-- This will NOT work in a multi-process or load-balanced environment as it depends on the current process state.