Remove the conflicting and mostly useless card.paused flag (the printing
is either paused, or not) and switch to isPrintPaused only which
accounts for both cases (SD/USB) correctly.
Fix M27/getStatus to show the current real status of the SD print.
Synchronize the queue on M601, as required to precisely pause the print
at the correct instruction.
Alias M25 to M601, which when combined with PR #1899 fixes issue #1614.
Guard against incorrect usage in M601, M602 and M603.
