Support for value replacement

[dougbrn]

Feature request
We have no easy way to allow the replacement of values in columns of data, without effectively rebuilding the dataset a la:

df_lc['label'] = df_lc.label.str.replace('MacLeod 16', 'CLAGN')

This is similar to #99.

Before submitting
Please check the following:

• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
• I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
• If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.

[dougbrn]

This is doable now with #135 , albeit while rebuilding the dataset. I think it's safe to close this and let another issue pop up if theres a real need for something more performant