Fix build for Qt5.11+

[JPTIZ]

It wasn't compiling for me (ArchLinux, Qt 5.12), so I did some research on how to solve the errors I had. Seems like Qt5.11 broke some obscure things here and there.

Changes:

• Fix missing '}' in QScintilla's project file (caught when running qmake for Qt4Qt5¹ directory);
• Fix error: invalid use of incomplete type 'class QAction';
• Add _build to ignore list (since it's mentioned on readme in build process).

¹Full path: nclcomposer/src/plugins/ncl-textual-view/deps/QScintilla_gpl-2.10.1/Qt4Qt5.

The spacing changes (trim trailling whitespaces on end of line) were done by my editor automatically on save.

This is probally my first contribution for a project that is not from a close friend, so, please check if it's all ok here, haha. :)