Speed up startup/primitive loading by replacing dict with unrolled tuple list

Before:
./som -cp Smalltalk TestSuite/TestHarness.som  0,01s user 0,01s system 4% cpu 0,538 total
After:
./som -cp Smalltalk TestSuite/TestHarness.som  0,01s user 0,01s system 56% cpu 0,027 total