cleanup
added rebar compiler (initial);
added persistent data for rebar compiler;
added ui for switching between rebar compiler and normal compiler;
fixed erlang compiler message parsing; fixed navigation to warnings and errors;
changed rebar importer: removed 'Compile' run configuration creation, set rebar compiler as default compiler instead;
changed rebar importer tests so that they check if rebar compiler is set as default compiler;
clear output directory flag is now unchecked by default for new projects;
changed rebar importer test so that it tests clear output directory flag is unset;