Allow base path to be configurable

[renaudboyer]

Web App path should be configurable at compilation time.

Every resource should be fetched from this path

App:

• [x] inbox
• [x] mailto
• [x] calendar
• [x] calendar-public
• [x] contacts
• [x] account
• [x] admin

Related to:

• https://github.com/linagora/esn-frontend-common-libs/issues/211