Fix typo in Error handling controller code

On the frontend, the error message 'Username already exist' appears when creating a user with the same username as an existing user.  Grammatically, this error looks strange.  A more proper error message would be 'Username already exists'.  Possibly later on support can be added to properly conjugate this error message for a 'plural' field.
Genericize invalid username or password message

https://github.com/meanjs/mean/issues/133
The message given to the user upon an invalid login attempt, for security reasons, should not reveal that the username or password was incorrect.  Rather, a generic message should be displayed when the username or password is incorrect.
Remove redundant variable declaration
Rise gunt-concurrent task limit.

Fixes issue with default value for grunt-concurrent limit in machines with few cpu/cores.

From grunt-concurrent docs:

	limit

	Type: Number
	Default: Number of CPU cores (require('os').cpus().length) with a minimum of 2

	Limit of how many tasks that are run concurrently.

In machines with few cpus/cores, the default limit of 2 the 'grunt debug' task
can't start enough tasks for starting the node-inspector task, so the command fails
and the capp can't be debugged.

Fixes issue #144
Fixed typo of div attribute
Use ng-annotate instead of ngmin
Tiny fixes

Removed double requires and unused variables.
Merge pull request #132 from macsj200/patch-1

Fix typo in Error handling controller code
Merge pull request #139 from macsj200/patch-2

Genericize invalid username or password message
Merge pull request #141 from NeverOddOrEven/remove-redundant-variable-declaration

Remove redundant variable declaration
Merge pull request #156 from miguelcoba/issue-144

Rise gunt-concurrent task limit.
Merge pull request #165 from neon5/master

Fixed typo of div attribute
Merge pull request #197 from Nepoxx/patch-4

Tiny fixes
Merge branch 'pr/177'
Small Update
Bump minor version
Merge pull request #1 from meanjs/master

merge original author update