Add categories

[jeanpimentel]

Some weeks ago people were trying to analyse our data and we figure out that we don't have categories.

TW Radar's has 4 categories: Techniques, Tools, Platforms, Languages & Frameworks.

Since we already use some categories (Technique, Tools, Language, Framework) at the knowledge map spreadsheet, I kept them and I also added the last one (Platform).
So, our categories are Technique, Tools, Language, Framework, Platform

• The system will continue to work with current data.
• The category will be required when editing a technology or when adding a new one.

We can think about a migration later, if needed.

[jeanpimentel]