Re-organized and improved categories

OpenStreetBrowser's main categories got a few improvements:

• A new category 'Memorials' which includes all monuments and memorials (which were part of the 'Historic' category).
• Also the 'Historic' category will no longer show wayside_crosses, wayside_shrines and wayside_chapels, these can now be found in the 'Religion' category.
• Instead of the 'Power' category, there's now a group of 'Energy' categories: 'Electric power', 'Coal', 'Petroleum and natural gas' and 'Renewables'.
• A new 'Railway Maxspeed' category. Both this and the 'Individual traffic maxspeed' category will now label the lines with the speed.
• All route relations (e.g. cycle routes, public transport routes, ...) now show the ref labels separated by ' · ', which is much easier readable.

If you have ideas for improvements for the categories, please post your ideas to the Github issues page.

Update 2018-10-27: I created another new category Power routes.