Add function to import data from other projects

[ChristinaSi]

There is one import dialog: You can choose the project to import data from. There are several options which part of the project you want to import:

• units

• units, recipes, articles -> additionally you can choose if you want to import recipes and articles with their tags

• units, articles -> additionally you can choose if you want to import articles with their tags

Additionally you can choose if you want to import the following:

• shop sections

• tags

You can not import meals.

[dboehmer]

Completed by 18dcb7d6.