added app icon, added "back" button to recipe creator. now creating recipes and adding them to the recipe manager

refactoring RecipeSearch, slight visual changes, now selecting ingredients in recipe creator and validating number inputs

Merging file manager into main

See merge request !1

# Conflicts:
#   src/main/java/mi/hdm/TastyPages.java
#   src/main/java/mi/hdm/controllers/BaseController.java
#   src/main/java/mi/hdm/controllers/HeaderController.java
#   src/main/java/mi/hdm/controllers/MainPageController.java
#   src/main/java/mi/hdm/recipes/Recipe.java
#   src/main/java/mi/hdm/recipes/RecipeSearch.java
#   src/test/java/mi/hdm/recipes/RecipeSearchTest.java

Split GUI and the model into two classes. File manager is now fully implemented. the branch will be merged with main

Deserialize methods in FileManager now take the JSON string as parameter. Fixed bug where empty files would cause NullPointerExceptions. All classes now work depend on an instance of TastyPages instead of static class members in TastyPages