Automatically detect "path" for a custom external tool

A custom external tool XML config has XML element "path".

It should have the following behavior:

• if path is not specified, the path of the imported XML config should be checked. If there is a file with name "binaryName" in this location, the tool path should be automatically set to the location+binaryName.
• if path is not specified, but there is no such file, then the path in the Application Settings should remain empty.
• it should be possible to specify an absolute "path".
• it should be possible to specify a relative "path". The location is relative to the XML config file.

Rename "binaryName" to "executableName".
Rename "path" to "executableFullPath".

Update the *.xsd schema in code like in the documentation.
If a toolkit is not specified, initialize the toolkit name to the same value as the tool name.

See also: https://ugene.net/wiki/display/UUOUM33/Custom+External+Tools.