Lazy loading of rows to support larger files

[krassowski]

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While I intended this extension to be a solution for editing small tabular files (but larger than it can be conveniently done in a text editor) like up to 20 columns and 200 rows, it might be useful to support larger files as jExcel does implement lazy loading. There are a few things to look out for though:

1. Search and replace needs to be carefully tested
2. The scrollbar will probably need to be switched to programmatic which can be sub-optimal for the UX (but this is what the CSV Viewer already does).

We could have a size threshold to automatically switch to lazy loading if a file is very big, but we may want to have an opt-out button.

For extremely large files we could use the lumino's datagrid as highlighted by @blink1073: example-datagrid. This seems to be "the future", but for now adopting jExcel may allow for more feature-rich experience.