Added client & server side validation for importing volunteer data

[raghavio]

This is for #85
Server side validation checks if

Email meets the regex and does not already exist.

Phone number is valid and does not already exist.

User has permission in the specified location.

If any of these conditions does not meet server sends back the failed imports as response to the AJAX request.

Client side validation check if

Email meets the regex

Phone number meets the regex

If it does not, cell turns red and that's it. You'll still be able to submit the data.

After submit: