+ Add FINE-level Log messages when truncation needed for the date to be valid

Remove comment in po files, this allow us to have a better understanding of what has changed in po files
in github history and while the PR that update translation is created.

The main issue here is whenever the code change, translation context change so updating a po file has a lot of unwanted changes in po files

Closes[/BS-16286](https://bonitasoft.atlassian.net/browse/BS-16286)

* check for nul values before converting
* add tests

Closes [BS-16274](https://bonitasoft.atlassian.net/browse/BS-16274)

- since 7.3 theme resources are accessed in a relative way using the URL
../theme. As a result, the path of the images declared in the CSS is
relative to the css directory in the theme so resources are not
retrieved from the war portal/ directory anymore.
We cannot remove them from there, though, because old forms look&feels
might still use them.
The solution is to just copy the two images we use inside the
appropriate directory in the theme.

Covers [BS-16006](https://bonitasoft.atlassian.net/browse/BS-16006)

Form V6 URL could be used to list all process instance variable values
by using a wrong ID (autogenerated form)

Covers [BS-15949](https://bonitasoft.atlassian.net/browse/BS-15949)

Covers [BS-15868](https://bonitasoft.atlassian.net/browse/BS-15868)

This method from Singleton class I18n was static, so could be called before
static singleton _INSTANCE was created, causing tests to fail, but not all
the time: depending on the order of the tests being run by Junit, the test
failed or not. Now this is not order-dependent.

* Revert "Feat/wildfly-restlet-patch (#108)"

This reverts commit ed2c1d9f43ca2de21d4ca87a94818f526b70fb8f.

* chore(restlet) upgrade restlet version to 2.3.9

- including restlet/restlet-framework-java/pull/1229 to avoid patching restlet
- follow restlet changes (preventing to set the Content-range as we want)

log level depends of catch exception during an exception on login
Add test to verify exception catch

Covers [BS-16221](https://bonitasoft.atlassian.net/browse/BS-16221)

Closes https://bonitasoft.atlassian.net/browse/BS-15466

replace servlet exception by error 401 when LoginFailedException was catch and redirect was false

Closes [BS-15873](https://bonitasoft.atlassian.net/browse/BS-15873)

- Call engine method to check if the user is a manager of an involved user when trying to display the overview form
- Make it configurable (inactive by default)

Covers [BS-16123](https://bonitasoft.atlassian.net/browse/BS-16123)

* feat(rest secu config): split REST API security configuration files to support:

* when reading from a .properties files, also read from -custom and -internal
files if they exist
* when writing a property, do it in the -internal file

Closes [BS-16126](https://bonitasoft.atlassian.net/browse/BS-16126)

* feat(rest secu config): code review feedbacks

* Take code review feedbacks into account

closes [BS-16081](https://bonitasoft.atlassian.net/browse/BS-16081)

Closes [BS-15913](https://bonitasoft.atlassian.net/browse/BS-15913)