MQE-1089: Allow usage of $ JavaScript variables in executeJs

[KevinBKozan]

Description

• <executeJs function=""/> now escapes $variable with \$variable (but not {$variable})

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/verification tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)
• Changes to Framework doesn't have backward incompatible changes for tests or have related Pull Request with fixes to tests

[coveralls]

Coverage increased (+0.02%) to 56.039% when pulling 23ed2c0 on MQE-1089 into dd9f789 on develop.