Change elemTypeParams to an idiomatic field

Change `elemTypeParams` from 0 to 1 values to `'consistent'` or `'lumped'`

For eg
```octave
elements(2).elemTypeParams = 1 ;
```

should change for:
```octave
elements(2).elemTypeParams = 'consistent' ;
```

Do for : 

- [x] Truss elements
- [x] Frame elements
