Pre-fill the LaTeX template path.

Index: src/control/settings/LatexSettings.h
--- src/control/settings/LatexSettings.h.orig
+++ src/control/settings/LatexSettings.h
@@ -18,7 +18,7 @@
 class LatexSettings {
 public:
     bool autoCheckDependencies{true};
-    fs::path globalTemplatePath{};
+    fs::path globalTemplatePath{ "${LOCALBASE}/share/xournalpp/resources/default_template.tex" };
 #ifdef __APPLE__
     std::string genCmd{"/Library/TeX/texbin/pdflatex -halt-on-error -interaction=nonstopmode '{}'"};
 #else