Add ability to create projects with multiple documents #148
Description
This should be done in multiple stages:
Stage 1: it is possible to create a project and aggregate files in it. The statistics is calculated as aggregation of all files in the project. The project is displayed in UI. All files not under a project are left under "Unnamed project".
Stage 2: it is possible to set up project TMs and Glossaries for the project. It is possible to upload new files in projects only. TMs and Glossaries are used in every file in the project.
Stage 3: it is possible to create a project and upload files in it on creation. There is a wizard to create projects and set everything up on creation step by step.
Stage 4: all other things are migrated using projects: substitutions, TMs searching, glossaries term management. It is impossible to upload files into unnamed project. There are no files left without a project. Unnamed project as an idea is eliminated completely. It is only possible to create projects and not separate files anymore.