LIFReader: Add User-Comment tags to the series metadata

Since there may be more than one User-Comment tag (unsure), I've added a [n] suffix (see below).  But this might be firstly unnecessary, and secondly does not perhaps fit in with the scheme used for the other element/attribute names.  The other issue I have here is that the comment text has had the newlines stripped AFAICT; not sure if that's from the w3c DOM API or with the input sanitising.  Is that important?

```
...
HardwareSetting|ScannerSettingRecord|nLineAccumulation 0: 1
HardwareSetting|ScannerSettingRecord|nLines 0: 5.2980575561528
HardwareSetting|ScannerSettingRecord|nPages 0: 5.29805755615234
HardwareSetting|ScannerSettingRecord|nRepeatActions 0: 50
HardwareSetting|ScannerSettingRecord|nSections 0: 43
Image name: test
Quantity|Unit 0: m
Quantity|Unit 1: m
Quantity|Unit 2: V
Quantity|Unit 3: V
Quantity|Value 0: 0.000000495
Quantity|Value 1: 0.0000006
Quantity|Value 2: 805.600061036088
Quantity|Value 3: 0
Reverse X orientation: false
Reverse Y orientation: true
User-Comment[0]: Test test test test  Entry entry entry  Test test test test```