Git: Support filtering log entries by author

+ quote arguments with potential spaces.

Change-Id: Ifd1bfecd7c30d145592432dff76c72024d2b1426
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/git/giteditor.h

@@ -51,6 +51,7 @@ public:
     void setPickaxeLineEdit(Utils::FancyLineEdit *lineEdit);
     QString grepValue() const;
     QString pickaxeValue() const;
+    QString authorValue() const;
     bool caseSensitive() const;
     void refresh();