Simple Weather Service - code cleaning and improvements

Add missing icons (heavy clouds, thunderstorm, snow).
Remove unneeded comparison operator (!=), improve conversion of Timestamp and MessageType, order includes.
Fix typo in documentation.
Remove not related change in StopWatch.

src/displayapp/screens/StopWatch.cpp

@@ -5,8 +5,6 @@
 
 using namespace Pinetime::Applications::Screens;
 
-constexpr int Pinetime::Applications::Screens::StopWatch::maxLapCount;
-
 namespace {
   TimeSeparated_t convertTicksToTimeSegments(const TickType_t timeElapsed) {
     // Centiseconds