Improve code style

[Borewit]

Changes:

1. Improve code style

2. Simplify opening URL by default browser

3. Remove unnecessary casting

4. Fix possible NullPointerException

5. Improve equals implementation in PlaylistTreeNode

[sonatype-lift]

MissingSummary: A summary line is required on public/protected Javadocs.

❗❗ 3 similar findings have been found in this PR

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File Path	Line Number
src/main/java/listfix/model/playlists/itunes/DictionaryParser.java	51
src/main/java/listfix/model/playlists/itunes/DictionaryParser.java	64
src/main/java/listfix/model/playlists/itunes/DictionaryParser.java	19

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[sonatype-lift]

NonOverridingEquals: equals method doesn't override Object.equals; if this is a type-specific helper for a method that does override Object.equals, either inline it into the callers or rename it to avoid ambiguity

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