Unsubscription & choose to receive a mail onStart / onEnd

- The subscription panel is placed in the "mysettings" menu (not anymmore a popup)
- A Unsubscribe button were added. It removes the email if found
- The 2 options to receive a mail when someone is starting to edit and finished to edit can be chosen for each user (at least one of the two is compulsory)
- First time you go on the email notification panel in the mysettings menu, a call is made to get the email and options already subscribed for this userId
  * If found, the form is pre-filled with the datas
  * If not, the form is set with defaults values
It's just informative. Users can still subscribe another mail for this userId.
- Removed the integration of this plugin in the "Share this pad" menu. First becaue, imo, it's not the place, and second, because it meant 2 forms with the same id.
Small corrections

- put back msgs to the debug level instead of info
- remove a call to ep_etherpad-lite/node/utils/Settings as it was for a function that doesn't exist anymore
- remove checked_state var for the form as I manage myself the default check for the options.
Changed tabs to spaces & removed trailing spaces
Added global option + malformed email + cleaning

- Added 'panelDisplayLocation' option to choose where to show the subscription form
- Manage malformed email (it crashed EPL)
- Brought back popup form to subscribe (with the new options + unsubscription)
- Popup form is a copy of the form in mysettings menu, so no more 2 html codes in 2 different places
- On unsubscription, only remove the email from "globalAuthor" row if the email is the same.
- Put all css styles in css file
- Some cleaning
Removed trailing space
Fixed when new settings not in settings.json
Added email confirmation for (un)subscription
A small correction to avoid a error generated in certain cases
Better management of the (un)subscription process
Not take into account the 'pending' section when finding users to send a mail to
i18n of the plugin (english & french for now)
forgot to commit i18n files + validation output page with template and external css
Tweaks: i18n in unicode format + nicer color for msg
Added test to var coming from settings.json file to avoid errors
if no settings for the pligin -> msg sent to the user
wIll I be invited by the king of my country now?
handling missing setting values

- default value given to panelDisplyLocation if missing instead of showing an error msg
- sending an error msg when user tries to use the plugin if settings are missing
- send a warn msg in the console on server start and when using the plugin if settings are missing
Cookie management
css correction
testing for i18n problems