Add tests for reading player data from a saved game

- Changed cPlayer::equip to a bitset
- Use a static constant instead of a loop to initialized player starting spells
- Only save spell points if the player has any (current if different from max)
- Symbolic forms for trait enum (and save symbolic forms also for skills)
- When loading a player, clear data which is not always present in the file
- Also add an init test for cPlayer

test/files/player/spells.txt

@@ -0,0 +1,6 @@
+MAGE 3
+MAGE 7
+MAGE 20
+PRIEST 2
+PRIEST 8
+PRIEST 60