Is your feature request related to a problem? Please describe.
It is proposed to migrate the Customizations Themes, Departments and Type to standard elements that the Decidim platform already offers.
The issue consists in:

• Migrate Themes to Scope
• Migrate Departments to Areas (that the title of areas is modified by Departments)
• Migrate Type to Scope: "Participació en normativa" will be the parent type and from here will hang both types that are currently as sub-scopes.

Describe the solution you'd like

• Add Areas to ParticipatoryProcess - Add Areas to ParticipatoryProcess #53 (Incloure a Decidim)
• A background process (Rake task) to migrate existing elements into new data structures.
  • Migrate Themes to Scope
  • Migrate Departments to Areas
  • Migrate Type to Scope: "Participació en normativa" will be the parent type and from here will hang both types that are currently as sub-scopes.
• Change Title of Areas to Departments - (gencat)
• Repeat existing filters by replacing them, if necessary (gencat)
• refer all existing associations. (gencat)
• Remove the FK (columns of BD) that point to the currently custom elements. (gencat)
• delete the tables and code related to Themes, Departments and Type. (gencat)

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

                  <child scopes>
                      +---+
                      |   |
                     0*n  |
+-----------+ 1   1 +-------+ 0 <interests>   +------+
| ScopeType |=-----*| Scope |*----------------| User |
+-----------+ 1   n +-------+ n               +------+
                       1=1
                        |
                        |
                       0*n
             +---------------------+
             | Participative Space |
             +---------------------+