Classes most worthy rename Cleanup/Modernizing

Since there seems to be more interest in cleaning up the codebase here are some opinions on
what would be easy to cleanup, harder, and not worth it.
Other longtime devs should weigh in these are just my opinions.

### **[READ THIS FIRST](https://qmcpack.readthedocs.io/en/develop/developing.html#qmcpack-coding-standards)**

### Some Files will be retained for the forseeable future in some manner.
```shell
src/Utilities
src/Numerics
src/QMCApp
# Almost any file with a copyright before #2019 is legacy and marked for death.
src/QMCDrivers
src/io
#except anything with `Estimator` in its name
src/QMCHamiltonian
# expect some opinions on naming
src/Containers
src/Platforms
src/spline2
```

### Others are unfortunately high traffic and/or contentious so you should check if they are being worked on.
```
src/Configuration.h
src/Estimators
src/QMCWaveFunctions
src/ParticleSet
```

Other files are legacy only or should be and working on them is low priority.
```shell
src/QMCHamiltonian/*Estimator*
# any WFC with no mw_ methods
src/QMCWaveFunctions/
src/einspline
src/spline
src/formic

```

**Describe the solution you'd like**
Adherence to "modern" naming conventions, improvement of variable names where they provide no aid to comprehension if possible.

**Additional context**
Potentially a good first issue.