Support for RFC-compliant TOTP hashes

[BryanJacobs]

This implements support for SHA-256 and SHA-512 hash algorithms when
generating TOTP codes. These algorithms are specified by RFC6238. The
implementation is compatible with Google's OTP URL format, as well as
with the KeeOTP plugin for KeePass.

The implementation is not wired into the GUI, as the main project
developer expressed strong negative sentiment about adding more
options there. It is possible to configure codes by putting the
appropriate string into the entry's otp property, or using another
program with a less opinionated UI and a compatible on-disk format.

Type of change

• ✅ New feature (non-breaking change which adds functionality)

Description and Context

Description above.

Fixes #873
Fixes #1566

Testing strategy

Built modified binary. Launched with existing database file containing a mix of SHA1 and SHA512 TOTPs from KeeOTP. Compared generated TOTP codes for both algorithms using "show OTP" with KeeOTP on one side and KeepassXC on the other. Ran OTP->"Show QR Code" and verified correct URL creation. Wrote and ran unit tests.

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED] - there is none, so I don't know what this is. But I've read every one that's in this repo.
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]
• ✅ I have compiled and verified my code with -DWITH_ASAN=ON. [REQUIRED]
• ✅ I have added tests to cover my changes.

[koutheir]

I think there should be a GUI option that comes with this new supported feature.

For the moment, if you wonder how to actually use the feature without any GUI support, then here is how I got it to work:

• Set up TOTP for the relevant entry as usual.
• Edit the entry and go to the Advanced left tab.
• Select the attribute TOTP Settings. Its contents are usually something like:

  30;6
  

  where 30 is the TOTP generation period in seconds, and 6 is the TOTP number of digits. Your content might vary depending on how you performed the TOTP setup.
• You will have to replace the content of the TOTP Settings attribute with a URL that can provide the same information, but can also specify the algorithm to use for TOTP. An example of the URL I used is:

  otpauth://example.com/?secret=MYTOTPSECRET&digits=6&period=30&algorithm=sha512
  

  Of course you will have to replace MYTOTPSECRET with your own TOTP secret. You can also replace example.com with a more relevant name.

Thank you @BryanJacobs for supporting the feature in the first place.

[droidmonkey]

Otp url should be in an "otp" attribute not TOTP Settings

[BryanJacobs]

Quoting from my original commit message, "The implementation is not wired into the GUI, as the main project developer expressed strong negative sentiment about adding more options there. It is possible to configure codes by putting the appropriate string into the entry's otp property, or using another program with a less opinionated UI and a compatible on-disk format."

I would rather have the feature be in keepassxc without GUI options than have it not be in keepassxc at all.

[droidmonkey]

I have an idea on how to add this to gui without bloating the dialog or confusing users.

[droidmonkey]

@koutheir and @BryanJacobs see #3622