simulator engine assets, styles and code

fixup!  * Fix escaping chars in FormGroup title  * Use lxml to produce XML view  * Update XMLToForm to follow escaping changes

some elements were double escaped.

See merge request nexedi/erp5!1621

It seems to accept int, but version is supposed to be a string.

See merge request nexedi/erp5!1671

a modified version from nexedi/erp5$366
that supports patterns like
DateTime(2001, 02, 03) => DateTime(2001, 2, 3)
and not DateTime(2001, 0o2, 0o3)

Javascript does not support big integers, so the backend have to be
careful not to return too large numbers in the json. Nowadays there
is bigint, but not equivalent for decimal numbers, so the backend
tries to detect if numbers are too big and returns them as string
in that case - which is better than returning a different number
because it displays correctly in the result table. The pivot table
will still wrong, but at least the table of results is OK.

use sax.xml API which gives us the first parser available, instead of
using a specific parser that happens to come from pyxml

serialize as json instead of using xml.marshal.generic which was
provided by PyXML

See merge request nexedi/erp5!1668

See merge request nexedi/erp5!1665

This allows custom movement generators to set ad-hoc properties on
generated movements depending on properties of the corresponding
input movement.

There was already _getUpdatePropertyDict which is similar, but was
sometimes not enough because it can only be use to set extra
properties on all movements.

As a result, when we needed a rule with custom properties on
generated movements, we resorted to overriding getGeneratedMovementList
and duplicating the full logic of the method. Existing cases have
been updated to use the new _updateGeneratedMovementList and in the
case of InventoryAssetPriceAccountingRuleMovementGenerator we no
longer need to duplicate the logic.

Also remove the comment suggesting overriding getGeneratedMovementList
in subclasses, now several "extension" methods exists, so it should
not be needed to override getGeneratedMovementList, every needs
should be coverred by defining _updateGeneratedMovementList or
_getUpdatePropertyDict