Add onPaste event and a flag to control the missing rows addition when pasting a data

[phen0menon]

This PR implements:

• Detect what cells (rows) have been changed after clipboard paste #175 issue feature
• autoPadRowsOnPaste flag which is considered to control whether the table should be extended when pasting a data out of table bounds or not

Any comments are welcome.

[coveralls]

Pull Request Test Coverage Report for Build 1279883980

• 1 of 10 (10.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.6%) to 78.963%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/actions.ts	0	1	0.0%
src/Spreadsheet.tsx	1	4	25.0%
src/reducer.ts	0	5	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/reducer.ts	1	48.87%

Totals
Change from base Build 1274895115:	-0.6%
Covered Lines:	727
Relevant Lines:	863

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💛 - Coveralls

[iddan]

Looks good! I’m on vacation until next week so I’ll try to go around it next weekend. Thank you

[phen0menon]

I found that it makes no sense to send row and column indices without value. There is one idea how to deal with that - I will reply to the thread within a few days.

And there is also the idea of ignoring 'readOnly' fields when pasting some values. I have implemented it locally, gonna send to review in a few days.

[iddan]

What about missing columns?