Support external tools downloading

1. External tools settings tab: for each tool add a new button "Download" near the "Browse" button. This button activates the downloading of its tool.
2. Tools data are downloaded to the temporary directory for updates downloads.
3. After downloading, the tools are installed (unpacked) into a special directory with all tools.
4. External tools settings tab: add a new setting for that directory that stores installed external tools.
5. When a tool is being downloaded:
   • The text "Downloading..." is shown instead of its path in the external tool settings.
   • The "Download" is disabled or invisible.
6. If a user wants to use an external tool that is not configured yet, a question message appears. Add the button "Download" to the message that activates downloading of the tool.
7. If a user wants to use an external tool that is currently being downloaded, a message with this information must be shown.
8. If a user updates UGENE using auto-update, all installed external tools must be updated too.

Different UGENE versions support different versions of tools. When a user click "Download" for a tool, UGENE must download the appropriate version of the tool.
The statistics about tools downloads must be updated:

1. UGENE downloads statistics on the server side
2. UGENE counters on the application side.