Bundle plants executable

[sverhoeven]

We got approval from the PLANTS author to ship the executable with a academic license.

We have to add a disclaimer to our license that the executable is only for academic purpose like

Included in PLANTS nodes plugin is the PLANTS executable with academic license (http://www.mnf.uni-tuebingen.de/fachbereiche/pharmazie-und-biochemie/pharmazie/pharmazeutische-chemie/pd-dr-t-exner/research/plants.html). 
By accepting this license agreement, you agree to use the included PLANTS executable only for academic usage.
To use these nodes in a commercial manner you need to acquire a valid license yourself and configure the PLANTS node to use the commercial executable

We need executables for

• Linux
• OSX
• Windows

The executables should not require additional installs like the openbabel library.

[sverhoeven]

Fixed in 951a350