Added Boyer-Moore string deletion algorithm as a fix for issue #286

[aryanVanaik]

Mandatory checks

• [x ] Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• [x ] Tests created for changes (if applicable)
• [ x] Manually tested changed features in running JabRef (always required)
• [ ] Screenshots added in PR description (for UI changes)
• [x ] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [ x] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

Closes #286

[koppor]

Closing this issue due to inactivity :zzz:

Please ping us if you intend to resume work on this one.