Remove language dependency from NBGL

[nroggeman-ledger]

Description

The goal of this PR is to remove the dependency existing between NBGL and languages:

• ids used to identify localized strings
• Global language_pack variable used in Fonts management library

This is a first necessary step to use NBGL as a common library for OS and Apps.

It only breaks compatibility with the OS (removed field in some objects, and nbgl_refreshUnicodeFont() prototype changed)

Changes include

• Bugfix (non-breaking change that solves an issue)
• [*] New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 48.48485% with 17 lines in your changes missing coverage. Please review.

Project coverage is 60.34%. Comparing base (fddeb90) to head (87aa7fd).

Files	Patch %	Lines
lib_nbgl/src/nbgl_fonts.c	48.48%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #750      +/-   ##
==========================================
+ Coverage   60.20%   60.34%   +0.13%     
==========================================
  Files          12       12              
  Lines        1729     1740      +11     
==========================================
+ Hits         1041     1050       +9     
- Misses        688      690       +2     

Flag	Coverage Δ
unittests	60.34% <48.48%> (+0.13%)	⬆️

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