add r aqp and soildb

[ocefpaf]

See https://cran.r-project.org/web/packages/soilDB/index.html and https://cran.r-project.org/web/packages/aqp/index.html

Ping @emiliom and @lsetiawan

xref: BiG-CZ/wshp2017_tutorial_content#14

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/r-aqp, recipes/r-soildb) and found it was in an excellent condition.

[ocefpaf]

Travis-CI is passing on my instance, merging this.