Textual improvements

A number of textual improvements/adjustments should be made. I'll list them below:

• Change 'enrollable' to 'open for enrollment' (student-dashboard)
• Also make the description about what this means clearer
• Change 'this course is enrollable by student' to 'Students can enroll themselves for this course' (CreateCourse). Maybe also add a tooltip for extra info here
• Typo in status box when review evaluation has already been claimed:
• 'Peer review your students' -> 'Peer review others' (LandingPage)
• Change note on allowed file types in HandIn.vue to 'File types allowed: pdf, zip, doc, docx'
• Change word order in the upload modal note in HandIn.vue to 'If you have already uploaded a file, this will overwrite the file!'
• Change 'unenrolled courses' to 'available courses' on courses page
• Descriptions in rubricwizard
• Move note about 'saving is not submitting' from notification to below buttons
• Capitalization in search bar Teacher and TAs
• Change 'The assignment is due yet' to 'The assignment deadline has not passed yet' in ReviewDistribution.ts
• Change 'There are already reviews assigned for this assignment' to 'Reviews have already been assigned in this assignment' in ReviewDistribution.ts
• Typo in 'uploading an new files'