[NLP/PC] add support for capitalization classes lower (L), upper (U), capitalize (C)
Signed-off-by: Iztok Lebar Bajec <ilb@fri.uni-lj.si>

# What does this PR do ?

While waiting for #3819 to be finished, upgrade of current punctuation capitalization model with support for lowercasing, uppercasing, and capitalisation. 

**Collection**: NLP/PC

# Changelog 
Modified the capitalisation decision from pure capitalisation, as soon as `capit_label` differs from noop (`O`), to one where the operation is based on three classes: lowercase (`L`), uppercase (`U`) and capitalize (`C`).

Warning: Due to the `class_label` previously used for capitalisation (`U`) and the way the decision was implemented prior to this PR, this change becomes a breaking change. Models trained prior to this PR will result in returning `all caps` instead of `capitalising` selected words. A retrain will, however, provide additional functionality.

# Usage
* You can potentially add a usage example below

**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [ ] Documentation

## Who can review?
@PeganovAnton 