Import coherentstate, thermalstate, displace, squeeze, wigner from QuantumInterface

[Krastanov]

Now that qojulia/QuantumInterface.jl#29 is merged, it would make sense to rely on that namespace for these helper functions.

[Krastanov]

ping @apkille

[apkille]

@Krastanov we get type piracy doing this, as the first four functions you mentioned dispatch on FockBasis, which is defined in QuantumInterface rather than QuantumOpticsBase. I missed this because FockBasis is not imported in the root file of QOBase and I was quick to assume it was defined somewhere in the package. Any ideas for fixing this?