Implement global rtl mode

lib/codemirror.css

src/display/selection.js

src/edit/CodeMirror.js

src/edit/commands.js

src/edit/options.js

src/input/ContentEditableInput.js

src/input/movement.js

src/line/line_data.js

src/measurement/position_measurement.js

src/model/Doc.js

src/model/document_data.js

src/util/bidi.js