[FIX] website.theme: need to convert xmlids into ids for write and reload theme
[FIX] website.theme: input are always checked for data with empty xmlid
[IMP] hr_timesheet, project: various usability-related improvements

hr_timesheet: merged use_timesheets and invoice_on_timesheets fields on account.analytic.account
that basically tells the same thing (project using timesheets). Propagated this change in
the various views using it.
project: various improvements in views to ease the user experience.
Merge pull request #2317 from odoo-dev/master-fix-theme-chm

[FIX] website.theme: need to convert xmlids; input are always checked