[IMP] Use radio widget in various views

+ some UI messages improvements

(Closes #1913)
[IMP] website.theme: add button in customize theme modal to show all theme modules
[ADD]Event: functionality of Event Mail Scheduler after subscription,before event and after event

[IMP]add access rule for event.mail and fix typo

[IMP]imporved code and labe

[IMP]updated cron job by 1 hour

[IMP]fix typo, apply group no one

[IMP]change onchange for one2many and set default value for boolean

[IMP]remove unused code

[IMP]add template for event mail schedule and test cases for the event mail scheduler

[IMP]indentation

[IMP]improve the code as per new api

[IMP]imporve the code for send mail

[IMP]improved sender mail in template

[IMP]improved sender mail in template

[IMP]fix variable declaration