Validate form

[Mehdi-Rh]

Premise

In this PR, I have implemented a client-side validation of the data in the contact form before submission imposing email characters to be lowercase.

Implemented interactions:

• When the user submits the form, you check if the email is in lower case.
• If the validation is OK, the form is sent.
• If the validation is not OK, you show an error message to the user near the submit button informing them of the error and the form is not sent.

Changes

• Add scripts/validateForm.js file.
• Add an error div if the email includes uppercase characters.
• Style the error div in the styles/mobile.css file.