Please, improve the use of categories for some small inconsistencies.

When running ./count_categories_and_tags.py | more from #2143 the output shows counts of categories and tags used. For counts of 5 and below, it also shows the icons names.

From this output, I would like to propose the following changes:

1. Rename Real World to Real world (which is also an existing category)
2. Rename Shape Arrows to Shape arrows to comply with convention
3. Rename UI and Keyboard to UI and keyboard to comply with convention
4. Rename UI to UI and keyboard