Support multiple Categories

[al-develop]

current: only one Category per Item
to implement: several categories per Item.

To Do:
DB

• create "Category" Table and add it to the creation script.
• adjust already existing entries: move all categories into to the new table. Add an CategoryId to the corresponding Item instead.

Code

• adjust the sql scripts to support the new table
• add a new Model for the new table
• add CRUD to the DataAccess for the new Table
• adjust the existing Entry Model, to have a CategoryId instead of a Category
• adjust the EntryViewModel to convert a Entry and a Category Model into the Category String and vice versa, separated by comma - thus the UI does not need to be changed.
• verify, that the Autofill can support the new feature.
• adjust eh CsvExport to support the new feature.
  • since the CsvExport uses models, instead of ViewModel, the Categories need to be concatenated into a string for the corresponding entry with a symbol which is support in csv (e.g. not necessarily a comma)

Users can then add several Categories to an Entry like this: Category1, Category2, Category3, ...
which is then being processed separately into the Models, and then inserted in two different Tables

Then, a new release can be build and uploaded