Reading non-numeric tags is NaN

When reading tags that are not of numeric type, the tag is converted to a NaN value. This is due to line 489 of webhandlers.py and can be resolved by just removing the line. The line attempts to convert the tag to a numeric value, but it really should first check that the tag is numeric in the first place or allow the user to specify which tags are numeric.

```
# Ensure non-numericals like "1.#QNAN" are returned as NaN
df["Value"] = pd.to_numeric(df.Value, errors="coerce")
```

https://github.com/equinor/tagreader-python/blob/master/tagreader/web_handlers.py