in all cases call getProtonCharge to get the proton charge
re #14323

We only need to load the logs for the measurement information.

Create synthetic nperiods log entry. The nperiods entry is present in the file, but not in the logs section. Having this will make the logs given to LoadEventNexus contain the same nperiods entry we currently have on the histogram workspaces.

The converted text is stored in separate .rst files in the docs directory.
Refs #9562

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>

LoadNexus, LoadNexusLogs, LoadNexusMonitors, LoadNexusProcessed,
LoadPDFgetNFile, LoadParameterFile, LoadPreNexusMonitors,
LoadRKH, LoadRawBin0, LoadRawSpectrum0, LoadRawHelper

re #6485

Introduced a helper class to perform this stuff and tidy up a lot
of copied code.