Add helper function to create version string

And remove all the duplicate code.

Depending on the situation prof_get_version() will return:
* 0.13.1
* 0.13.1dev
* 0.13.1dev.master.69d8c1f9

src/common.h

@@ -180,4 +180,6 @@ gchar* get_expanded_path(const char* path);
 void glib_hash_table_free(GHashTable* hash_table);
 char* basename_from_url(const char* url);
 
+gchar* prof_get_version(void);
+
 #endif