Enable CodeChecker plugin only for C/C++ projects

[dkrupp]

Today it is disturbing that codechecker is showing popups/warnings for non C/C++ project.

• If a project is opened which does not contain at least one C/C++ file, dont display any notifications about missing compilation database (as is done currently)
• dont run codechecker analysis/parase at all (on file save) while compile_commands.json is not available
• for non c/c++ projects the sidebar overview should display "CodeChecker is only available for C/C++ projects"
• if CodeChecker detects at least one C/C++ files and compile_commands.json is not available the popup notification can be shown as today and in the sidebar overview we should only display a text "Compilation datatabase is not available. You can configure one here (instead of the current reanalyze current file etc. which would not work anyway).