Tracks may have tracknumber and discnumber formatted as "x/y" where:

- x is the current track/disc number
- y is the total number of tracks/discs

For example this is the case for tracks downloaded from Google Play
Music. Now `parse_resource` function considers this particular case,
otherwise will stick with the normal behaviour

Since date tag inside tracks is a string, it can have any possible
value. Previous code tried to parse date as an integer, but for example
strings such as "2017-11-12 14:34" can't be cast to an integer value.

As a workaround, date is now parsed as is, and the application client
should handle its value as it sees fit