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.
* Eliminate TOTP logic from GUI elements
* Consolidate TOTP functionality under the Totp namespace
* Eliminate guessing about state and encoders
* Increased test cases
* Add entry view column for TOTP [#2132]
* General code cleanup, reduction of unnecessary steps, separation of concerns
* Rename SetupTotpDialog to TotpSetupDialog for consistency
* Add the concept of custom TOTP encoders, each with potential for custom
code alphabet, length, step interval and code direction (i.e. reversed)
* Select custom encoder via overload of the digits field of a loaded entry
* Allow selection of custom encoders via the "TOTP Settings" field's
size, as currently done by KeeTrayTOTP for Steam. Use "S" for the
short name of the Steam custom encoder
* Allow selection of custom encoders via the "otp" field by appending
a "&encoder=<name>" field to the URL query. For example,
"&encoder=steam"
* Update TOTP set-up dialog to permit selection between (default,
steam, custom) settings.
