Implemented functions for extract signatures and split fee payer

[jimni1222]

Proposed changes

This PR introduces new functions in makeRawTransaciton.js file named 'extractSignatures' and 'splitFeePayer'.

extractSignatures function extracts signatures and feePayerSignatures from rawTransaction.
splitFeePayer function deocde rawTransaction and make fee payer tx format.

And also deocdeRawTransaction function is modified to call _decodeFromRawTransaction.
Because when combine raw transaction string(not included in this PR), transaction have to compare with other transaction string.
For easier comparison, _decodeFromRawTransaction returns string format of accountKey without parsing.

Types of changes

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• Bugfix
• New feature or enhancement
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Related issues

refer #117

Further comments

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