Change text references from "arguments" to "subcommands"

[toadkarter]

Fixes #3226

CHANGES
This PR changes text references in the --help command screen from "arguments" to "subcommands". The change is propagated to variable names in the code to avoid confusion where appropriate.

There are also some changes in the subcommand description text to match the man page more closely.

TESTING CRITERIA

1. Open the help screen with the command flameshot --help.
2. Notice that instead of references to "arguments", there are now references to "subcommands".
3. Notice that descriptions for "full" and "screen" subcommands have been updated to cover scenarios relating to multiple monitors.

If you would like me to make any changes please don't hesitate to let me know.

[mmahmoudian]

Thanks, at first I thought this is easy for me to review, but because the variable names are also changed, I cannot approve this myself. Lets let @veracioux review this PR

[toadkarter]

Thanks, at first I thought this is easy for me to review, but because the variable names are also changed, I cannot approve this myself. Lets let @veracioux review this PR

No problem! I had initially intended just changing the text but then thought it might be confusing for anyone working on the code in the future if the variables were still called by the old name. I have no issues changing the names back to their originals though if needs be!

[toadkarter]

Hmm, is that appimage failure something on my end?

[mmahmoudian]

@toadkarter

Hmm, is that appimage failure something on my end?

No, that is a CI from our side that is failing to work and we have not yet managed to find time to figure out the issue. Don't worry about it.

Thanks for the PR and all the efforts 😃