Some translation stuff

Added some more lines to language_eng.php and language_nl.php. However, the way translations will done will be changed (check rest of commit)
Added a new plugin to Smarty: block_t.php. This plugin allows you to use the {t}{/t} block, which are translatables
Added extract.sh and compile.sh, which are two scripts that scan your project for translatable text
Added Smarty Gettext library, which enables the use of translatables in your project

(Credits to C. Poppema for showing me this)
Minor additions and changes

Controllers:
Changed some commented text in security.php
Changed an if statement in multitenancy_writer.php

Views:
Added some translations which I forgot last time
Added edit comment(s) feature to completed feedback and changed some stuff regarding the feedback

Controllers:
Added edit_feedback and edit_feedback_post functions to feedback.php
Added feedback edit routes to index.php

Views:
Added edit_feedback.tpl
Added an is_positive property to each competency in feedback_form.tpl, which will later be used to display graphs which separate positive competencies from points of improvement
Added a bit of client side validation for feedback_form.tpl, so someone doesn't lose all their data incase not all ratings are filled in
Added an edit button to the feedback_overview.tpl when someone completes a review
Changed some stuff regarding the reports

report.js:
Average ratings now have a different tooltip, which displays the amount of ratings of that competency

report.php:
Added an if statement to check if a comment is empty, which is then used to hide the matching tab if a competency doesn't have any comments

report.tpl
Added some extra text to a comment if the reviewee ID matches the current user ID
Tabs for competencies that don't have any comments will now be hidden