Remove bluemonday and fix double-escaping

[david-bezero]

Fixes #183

Uses json.Marshal to build a correctly encoded user structure (replacing fmt.Sprintf), removing bluemonday from this part of the code entirely as it is not required.

Also updates the email template code to avoid double-encoding everything, and removes bluemonday as it is not necessary (any tags entered are encoded by the template library anyway, as seen in the test, so there is no risk of injection)

This preserves the whitespace / trimming tidy-up steps for the email data.

[david-bezero]

I'm not sure what to make of the linting error but it's not related to anything that changed in this PR:

G101: Potential hardcoded credentials: RSA private key (gosec)

(file: provider/apple_test.go)

[paskal]

@david-bezero, please rebase from the master to fix tests. Are there any changes expected in this PR based on previous comments, or it's in the final state for the review?

[paskal]

@david-bezero, gentle ping for an answer.

[david-bezero]

hey. Sorry I don't have time lately to update this PR, but to answer your question as far as I'm aware this is in a good state to review.

I can maybe rebase it some time next week.

[umputun]

Could you pls resolve the conflict? I'm going to merge it in and release a new version as soon as it done

[david-bezero]

Sorry for the delay; I've been away over the holidays. Rebased and force-pushed.

[coveralls]

Pull Request Test Coverage Report for Build 7463747212

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 82.746%

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Totals
Change from base Build 7265392742:	-0.2%
Covered Lines:	2561
Relevant Lines:	3095

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💛 - Coveralls