Move ItemListTable-Element outside of page.py

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.
Do not always import module used only in debug mode
Do not import lxml in headers of page.py
Do not import exceptions of requests / load browser if needed

The import process of requests is very expensive: it imports all urllib,
and a lot of stuff. It is a problem on slow hardware, for applications
not running browser2 (example: weboob-config update).

This patch has two mains parts:
 * introduces load_browser to load a browser only if needed (a lot of repository
   processing does not need a browser)
 * Do not import exceptions of requests, but use Weboob internals one

Before: 6455 open/190 modules imported
After: 3997 open/112 modules
Do not import/export dates utils in misc
Well, we *never* do i18n
Move the import oh html2text outside of misc
Do not import Date in results header

Actually, the condition are not widely used. Do not load the datetime
module if we don't run it.
Introduce local exception for SSL errors

It removes the import of SSL in console applications (SSL -> socket ->
base64 -> ...)
DateField/TimeField/Delta are not really a base object
Revert part of "import module used only in debug mode"

Since the date are now not always imported, it does not make a lot of
sense to not import all date utils
Some missing renames of ICap to Cap

refs #1424
Some English fixes

"informations" is incorrect; try to use a better word, or the invariant "information".
s/IBaseCap/CapBase/ (refs #1424)
s/BaseCapObject/BaseObject/ (error in documentation)
Fix a regression: restore ListItem version

And move it in the same place than before to help the diff...
Add missing import
Import of FormFieldConversionWarning can not fail anymore

The test was here for python3 user, to not import browser1.
Since the load of the exception does not need browser1 anymore (see
"Remove import of browser1 in BaseApplication"), this check is useless
add LBP to currencies
possibility to set custom separators for decimals