Rename scan command to malware-scan

[akenion]

With the addition of the vuln-scan command in #64, it is no longer apparent that the existing scan command solely scans for malware and not vulnerabilities. It should be renamed to malware-scan to avoid any ambiguity.

Additionally, if scan is invoked after this change, it should inform the user that the scan command has been renamed.

[ewodrich]

Verified the message "The "scan" subcommand has been renamed to "malware-scan" " is returned when the command wordfence scan is invoked. Repeat tested somewhat at random with a variety of available malware-scan options. General testing of the malware-scan command is in progress to verify the options with the new command name are continuing to work as expected.

One issue was found with the option wordfence scan --help or -h where it returned the following, however this is to be addressed in Case #85 .

usage: scan [-h]
options:
  -h, --help  show this help message and exit