Signatures using the Core SDK

[germartinez]

Context:

The SDK team is updating the documentation to explain how to create signatures using the Safe{Core} SDK:

• Utilities to generate signatures using the SDK
• Signature collection to execute Transactions or to sign Messages
• Signature collection using the SDK and Safe Services
• on-chain vs off-chain messages

Note:

This PR cherry picks all the commits from #313 as that PR was created from the wrong base branch. This one is using development after nextra was squash merged.

[github-actions]

Overall readability score: 68.54 (🔴 -0.21)

File	Readability
signatures.md	62.73 (-)

View detailed metrics

🟢 - Shows an increase in readability
🔴 - Shows a decrease in readability

File	Readability	FRE	GF	ARI	CLI	DCRS
signatures.md	62.73	55.44	9.92	12	12.41	6.59
	-	-	-	-	-	-

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	68.54	58.79	9.22	9.85	10.63	7.08
	🔴 -0.21	🔴 -0.03	🔴 -0.04	🔴 -0.05	🔴 -0.04	🟢 +0

View metric targets

Metric	Range	Ideal score
Flesch Reading Ease	100 (very easy read) to 0 (extremely difficult read)	60
Gunning Fog	6 (very easy read) to 17 (extremely difficult read)	8 or less
Auto. Read. Index	6 (very easy read) to 14 (extremely difficult read)	8 or less
Coleman Liau Index	6 (very easy read) to 17 (extremely difficult read)	8 or less
Dale-Chall Readability	4.9 (very easy read) to 9.9 (extremely difficult read)	6.9 or less

[germartinez]

Notes:

• Acording to the code style in the docs all semicolons should be removed.
• "Safe Account" should be writen this way: "Safe account" or just "Safe".

[yagopv]

@germartinez all the suggestions and comments were addressed