Create Database Consistency category

[joaomarcos96]

I'm not sure "Database Consistency" is the appropriate term here since there is already a gem with that name, but I couldn't find another term that conveys the same meaning. Feel free to suggest another one.

[colszowka]

Thanks @joaomarcos96, I think having this category makes a lot of sense, I've had this on my todo list list for quite some time since there's a range of gems that I really like to use and we should add those there as well I think:

• https://www.ruby-toolbox.com/projects/rein
• https://www.ruby-toolbox.com/projects/hairtrigger (technically, trigger functions don't neccessarily belong to the consistency theme but I sometimes use them for exactly that)
• https://www.ruby-toolbox.com/projects/strong_migrations

We should then probably widen the description a bit, I'd suggest something like the following, what do you think?

Tools that aid in enforcing database consistency, finding issues with your migrations or differences between your tables and models

[colszowka]

I'm merging this and will follow up with another PR with the adjustments I suggested above