Add possibility to ignore files e.g. .htaccess or files that need to stay

[a-tonchev]

[simonh1000]

These PR requires an explanation of what it is trying to do, and it also needs more information in the README

[a-tonchev]

@simonh1000 This PR makes it possible to preserve files on the server (and not remove them), e.g.:

config = { preserve: [".htaccess", "/keepThisDirectory", "/toKeepDirectory/keepFile"] }

This will remove everything else than the files and directories included in "preserve"

[a-tonchev]

Will this be merged soon or is there need of anything else?