EZP-21348 eZOE: table width not saved in IE8

JIRA: https://jira.ez.no/browse/EZP-21348

*Note: the topic branch for this PR was created from the branch `ezp-21346_ie8_cell_merge` used in the PR #703 to ease merging of the unit tests changes, only commits be86846 and 47e229b are relevant here*

# Description

Like in #703 (see [EZP-21346](https://jira.ez.no/browse/EZP-21346)), it's a case issue. In IE8, Online Editor adds `style="WIDTH: XXXX"` to set the width a table which is transformed into `WIDTH="XXXX"` and then removed because the parser expects the attribute name to be in lowercase. This patch makes sure the `width` attribute (actually any attributes from the CSS style) is added in lowercase.

# Tests

manual + unit tests