[WIP] Added detailed repr and str

Current output:

```
In [5]: t
Out[5]: 
<mdtraj.Trajectory with 1 frames, 4091 atoms, 254 residues at 0x5695bd0>

Containing topology:

<mdtraj.Topology with 1 chains, 254 residues, 4091 atoms, 4139 bonds at 0x4b26e50>
        name element  resSeq resName  chainID
serial                                      
0         N       N     267     LEU        0
1         H       H     267     LEU        0
2        H2       H     267     LEU        0
[...]
       name element  resSeq resName  chainID
serial                                      
4088      C       C     520     PHE        0
4089      O       O     520     PHE        0
4090    OXT       O     520     PHE        0

In [6]: print(t)
<mdtraj.Trajectory with 1 frames, 4091 atoms, 254 residues>

Containing topology:

<mdtraj.Topology with 1 chains, 254 residues, 4091 atoms, 4139 bonds>
       name element  resSeq resName  chainID
serial                                      
0         N       N     267     LEU        0
1         H       H     267     LEU        0
2        H2       H     267     LEU        0
[...]
       name element  resSeq resName  chainID
serial                                      
4088      C       C     520     PHE        0
4089      O       O     520     PHE        0
4090    OXT       O     520     PHE        0

In [7]: 
```