## Context
After deprecating BlueConfig files, we no longer support legacy node
format, MVD3 or NCS. Therefore, this PR removes the corresponding node
loaders.

## Scope
In `cell_reader.py`: keeping only `load_sonata` and removing the other
readers.
In `metype.py`: removing `Cell_V5`.


## Testing
Adapt the current unit tests to use SONATA nodes.

## Review
* [x] PR description is complete
* [x] Coding style (imports, function length, New functions, classes or
files) are good
* [x] Unit/Scientific test added
* [x] Updated Readme, in-code, developer documentation

## Context
Addresses BBPBGLIB-1124.
Removes code related to hoc targets, as well as the need of using a hoc
TargetManager.

## Scope
Few functions were implemented in the python Targetmanager in order to
remove the hoc version:
getMETypes(), getPointList() and location_to_point()

## Review
* [x] PR description is complete
* [x] Coding style (imports, function length, New functions, classes or
files) are good
* [ ] Unit/Scientific test added
* [ ] Updated Readme, in-code, developer documentation

## Context
After removing BlueConfig, we only support SONATA edges files loaded via
`libsonata` API. This PR removes the synpase loaders that were used to
support non-SONATA files.

## Scope
Remove `SynapseReader.mod`. 
In `synapse_reader.py`, remove class `SynReaderNRN` which was used to
load non-SONATA .h5 files via `HDF5Reader`.

## Testing
Remove the test for `SynReaderNRN`

## Review
* [x] PR description is complete
* [x] Coding style (imports, function length, New functions, classes or
files) are good
* [ ] Unit/Scientific test added
* [x] Updated Readme, in-code, developer documentation

…th errors (#120)

## Context

In the simulation config, synapse_configure contains HOC code.
Neurodamus should fail fast when there is an error in configuration,
instead of passing it forward.

## Scope

Error check is added to connection.py

## Testing

TBD

## Review
* [X] PR description is complete
* [X] Coding style (imports, function length, New functions, classes or
files) are good
* [x] Unit/Scientific test added
* [N/A] Updated Readme, in-code, developer documentation

## Context
After the deprecation of BlueConfig files, out.dat is not generated
anymore.
Remove the SpikeWriter mod file and the code that was handling the old
out.dat spike file.

## Review
* [x] PR description is complete
* [x] Coding style (imports, function length, New functions, classes or
files) are good
* [ ] Unit/Scientific test added
* [ ] Updated Readme, in-code, developer documentation

This reverts commit c95917b.