Add ability to load assets from another template

Use case : 
    If you want to easily manage several Thelia2 instances based on the same template 'baseTemplate' 
    And you just want to customize derived templates via smarty block extends
    While style being able to add a functionnality to all thelia2 instances easily by only modifiying 'baseTemplate'

Arbo example:
instanceThelia2_1/
    templates/
        frontOffice/
            Instance1/
            baseTemplate/

instanceThelia2_2/
    templates/
        frontOffice/
            Instance2/
            baseTemplate/



- adding param 'template' to
    {javascripts file='assets/js/libs/jquery.js' template='baseTemplate'}
    {stylesheets file='assets/less/styles.less' filters='less'  template='baseTemplate' }
    {images file=assets/img/picture.png' template='baseTemplate'}

Keep up the good work