Already installed sound packages are not detected properly

Currently, at first install, the installer looks for a file named something like .asterisk-core-sounds-en-ulaw-1.5 in the sounds directory. If it's found, the installer tries to run Soundlang::installPackage() which fails because there's no package ID passed to it. I'd suggest doing a lookup for matching packages in the database, which can then be marked as installed.

(Also, not sure if it's intentional or not, but the existing sound files would be overwritten by the installer anyway, as the previous block of code is downloading from the server. Should the check for existing packages be placed before this?)