Add ChihuahUI and add CSS for index and login page

backend/build.gradle.kts

backend/src/main/java/server/service/SetUpService.java

backend/src/main/resources/css/index.css

backend/src/main/resources/css/main.css

backend/src/main/resources/templates/account.html

backend/src/main/resources/templates/createNew.html

backend/src/main/resources/templates/dashboard.html

backend/src/main/resources/templates/error.html

backend/src/main/resources/templates/header.html

backend/src/main/resources/templates/index.html

backend/src/main/resources/templates/login.html

backend/src/main/resources/templates/modifyCourse.html

backend/src/main/resources/templates/privacypage.html

backend/src/main/resources/templates/setUpGroups.html

backend/src/main/resources/templates/setUpProject.html

backend/src/main/resources/templates/setUpTAs.html

backend/src/main/resources/templates/statistics.html

backend/src/main/resources/templates/statsDisplayed.html