Add a possibility to use some UGENE inner variables in the command execution string in the "Configure Element with Command Line Tool" dialog

The "Configure Element with Command Line Tool" dialog has an "Execution string" input field at the last page. One can enter an explicit command with arguments that will be used to launch the tool. Currently, all paths are supposed to be hardcoded or they should be relative to the UGENE binary (or to the workflow output folder, actually, I don't remember). It should be possible to use some UGENE inner variables that will be defined right before the task launch.
The following variables should be supported:

1. Path to python. It should be taken from the UGENE settings.
2. Path to java. It should be taken from the UGENE settings.
3. Path to R. It should be taken from the UGENE settings.
4. Path to perl. It should be taken from the UGENE settings.
5. Path to the UGENE "tools" folder. Be careful, there may be no such folder e.g. in case of the standard package.

The variables should be marked with the percent signs on both sides of the variable name: %VARIABLE_NAME%.