Pass an input string "as it is" to a workflow element with a command line tool

Allow a user to pass a string "as it is", not "as a text file" to a workflow element with a command line tool. In conjunction with UGENE-817 this should allow a user to pass any input files to the command line tool.

The following changes in the GUI are required. In the "Create Element with Command Line Tool" dialog, on the second page:

• "Format" in "Input data" should be renamed to "Read as".
  There should be two values: "Text file" (currently, it is "Plain text") and "String value"

• "Format" in "Output data" should be renamed to "Write as".
  Leave here only one value "Text file" (currently, it is "Plain text").