Update includes to to be relative to src directory

Don't use relative imports like `../foo.h` as those depend on the
relative position of both files. Rather than that use imports relative
to the `src` directory, which explicitly is part of the include
directories.

src/displayapp/screens/Alarm.cpp

@@ -15,9 +15,9 @@
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
-#include "Alarm.h"
-#include "Screen.h"
-#include "Symbols.h"
+#include "displayapp/screens/Alarm.h"
+#include "displayapp/screens/Screen.h"
+#include "displayapp/screens/Symbols.h"
 
 using namespace Pinetime::Applications::Screens;
 using Pinetime::Controllers::AlarmController;