Use GNOME's default avatar

https://bugzilla.gnome.org/show_bug.cgi?id=720734
Merge branch 'feature/show-anonymous-avatar-by-default' into t
Merge branch 'feature/show-diff-renames' into t
Merge branch 'feature/diff-progress-bar' into t
Merge branch 'feature/show-detached-head' into t
Merge branch 'feature/commiter-info' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.html
Merge branch 'feature/hunk-scope-info' into t
Merge branch 'feature/more-file-stats' into t
Merge branch 'feature/file-header-collapsing-toggle' into t
Merge branch 'feature/add-collapse-all-button' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.html
Merge branch 'feature/improve-diff-view-styling' into t

Conflicts:
	libgitg/resources/diff-view.css
Merge branch 'feature/improve-diff-view-styling' into t

Conflicts:
	libgitg/resources/diff-view-html-builder.js
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.html
Merge branch 'feature/improve-diff-view-styling' into t

Conflicts:
	libgitg/resources/diff-view.css
Merge branch 'feature/separate-commit-message' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.html
Merge branch 'feature/separate-commit-message' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.html
	libgitg/resources/diff-view.js
Merge branch 'feature/keep-scrollbar-at-bottom' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.js
Merge branch 'feature/keep-scrollbar-at-bottom' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.js
Merge branch 'feature/keep-scrollbar-at-bottom' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.js
Merge branch 'feature/separate-commit-message' into t

Conflicts:
	libgitg/resources/diff-view.css
	libgitg/resources/diff-view.html
Show and scroll message body with the commit diff