New acc variant for Slovak language

Based on cz(ucw). Slovak letter frequency is used if a letter can be used with multiple diacritic symbols. Other accented letters of Slovak and Czech language end up on surrounding unused keys.

I have been using this layout for about 9 years now as a downstream patch. I just got tired of backporting it after each update of distribution package.

I have used base in a hope that it could have similar group of users like ucw that is in base as well.