* vcard: Fix whitespace handling in line cont's
Previously, multiple whitespace characters at the start of a
continuation line would all be dropped, instead of only the first one.
Also,
- restrict line continuation characters to SPACE and TAB.
Note that, like before, this identifies the CR (`\r`) character with the
empty string, and thereby notably does not require a CRLF (`\r\n`)
sequence (which is mandated by RFCs 2426, 2425) for line termination
(i.e., `\n` suffices).
Fixes: Bug 1 of issue #9593.
* vcard: Add test for #9593/1
* Fix coding style
Fixes composer dependencies: Package phpunit/phpunit-mock-objects is abandoned
We cannot support v8 yet because of errors like:
Declaration of MailFunc::setUp() must be compatible with PHPUnit\Framework\TestCase::setUp(): void
It would require dropping PHP < 7.1 support.
