workbench: added option to let git decide which files to display

[lpaulsen93]

In the directory settings it is now possible to choose between a workbench or a git file filter. The later is new and lets git decide which files to display depending on the contents of the .gitignore file.

This also adds a new function to the utils-lib called gp_filelist_scan_directory_callback().

See this example screenshot:

[lpaulsen93]

I need some help or advice regarding Travis CI. The build of the workbench plugin failed with this error message:

../../../workbench/src/plugin_main.c:28:18: fatal error: git2.h: No such file or directory
 #include <git2.h>

I found this comment in the Travis CI config:

    # Ubuntu 12.04 doesn't have libgit2, 14.04 has a too old one, so we build
    # our own for now.
    #- libgit2-dev

On my local machine I have libgit2-dev installed and can build without problems (Ubuntu 18.04.2). How can I fix this issue?

[elextr]

There seems to be a logical error in the .travis.yml, the presence of a .pc file for libgit2 is tested here but that doesn't check the version, it just accepts any version.

But that doesn't seem to be the issue here since it doesn't seem to execute the echo in the then clause or the build in the else clause, weird.

[lpaulsen93]

@elextr: the issue was caused by an incomplete makefile in the workbench plugin. It missed $(WORKBENCH_CFLAGS) in the workbench_la_CFLAGS. The result was that building it locally on my machine worked, but the Travis CI build failed.

[lpaulsen93]

Waited 3 weeks an Travis builds are fixed. So I merge this now.