fixed #188 - [OPENMEETINGS-2774] Improve the mails (template) design

[geoffreylgv]

Three HTML files edited with new design for mails

• RegisterUserTemplate.html,
• InvitationTemplate.html, and
• ResetPasswordTemplate.html

Here you can find the view of the test :

[solomax]

Thanks for the contribution @geoffreylgv

Updated version will be available at CI https://ci-builds.apache.org/job/OpenMeetings/job/openmeetings/ (in couple of hours) and at demo server https://demo-openmeetings.apache.org/openmeetings (in about a day or so)

[geoffreylgv]

It is a real pleasure, thank you too; because, I learned a lot through this contribution.