[IMP] l10n_pl: some corrections in Polish CoA

PLN as default currency
Many improvements in taxes and fiscal positions
Fixes #825
[ADD] web_pdf_viewer: PDF in-browser preview

This module extends web client and reporting tool in order to allow a
preview of PDF files directly in the browser (if supported by the
browser). If you disable it, standard file download stays available.
[FIX] google_calendar: browse user as SUPERUSER_ID to be able to write/update google_calendar info on user
[FIX] web_tip: scroll if needed prior to displaying a tip
[IMP] sale,purchase: allow invoicing

(closes #500)

(cherry picked from commit 84c0595aef3a417702c81b5226ae1f61817a2bf8)
[IMP] Event: Split Tickets
Attendees are created on SO confirm.
Attendees are directly created for FREE registrations and
Attendees are created and SO are linked to the paid tickets.
Improved code to make (5 attendees lines, 2 SO lines) when 3 vip tickets and 2 standard tickets are bought.

This commit fullfills the following Goals:

Goal 1 : When only website_event is installed, free registration should be possible from website.
Goal 2 : When only event and website_event are installed, badge report should be print for free registrations.
Goal 3 : When website_event_sale is installed, at that time on confirming the sale order, the subscription line are splited per attendees.
Goal 4 : Added code for attendees registrations through SO. Now from SO also the attendee's details for the event can be filled same as from website