[calendar] add timezone parameter to calendarevent in order order do get the good date/hours in ical exports

weboob.tools.browser -> weboob.deprecated.browser
weboob.tools.parsers -> weboob.deprecated.browser.parsers
weboob.tools.mech -> weboob.deprecated.mech
weboob.browser2 -> weboob.browser
weboob.core.exceptions -> weboob.exceptions

Also, the new tree for browser2 is:

weboob.browser: import weboob.browser.browsers.* and weboob.browser.url.*
weboob.browser.browsers: all browsers (including PagesBrowser and LoginBrowser)
weboob.browser.url: the URL class
weboob.browser.profiles: all Profile classes
weboob.browser.sessions: WeboobSession and FuturesSession
weboob.browser.cookies: that's a cookies thing
weboob.browser.pages: all Page and derivated classes, and Form class
weboob.browser.exceptions: specific browser exceptions
weboob.browser.elements: AbstractElement classes, and 'method' decorator
weboob.browser.filters.*: all filters

They bring nothing of value (we never use import * anyway) and introduce
a maintenance burden.

The __all__ that I left might not be very useful either but at least
they are not a pain to maintain; they are also used by pyflakes in some
cases.

This makes nosetests optional at least in theory.
Recent nose versions already do the same thing internally.

One of the goal is to not import all modules needed by filters by
loading the page file.

In the same goal, move the import of parsers in the class definition.