Le-utils

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- Added the following language codes:
- ach = Acholi
- fuv = Fulfulde Mbororo
- xog = Soga
- tuv = Turkana
- lwg = Oluwanga
- nyn = Nyankore
- myx = Masaaba

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- Duplicated python constants/ definitions as json files under resources/ (for easier integration with frontend)
- Added tests to make sure python constants are in sync with json constants
- Implemented first_native_name helper (used to set channel names in chefs)
- Added list-like `convertible_formats` attribute for all presets
- Added `html5_dependency` and `video_dependency` presets
- Updated constant mapping with epub -- The EPUB preset is used with document content type
- Added the following language codes:
- und = Undefined
- mul = Multiple languages
- arq = Algerian; Darja
- lkt = Lakhota; Lakotiyapi; Teton
- hdy = Hadiyya; Hadiya; Adea; Adiya; Hadia
- sid = Sidamo; Sidaamu afii; Sidaama; Sidama
- wal = Wolaytta; Borodda; Uba; Ometo

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- Added file format constants for ePub
- Added RTL language lookup table in le_utils.constants.languages.RTL_LANG_CODES
- Added the following language codes:
- be-tarask = Belarusian
- hrx = Hunsrik
- lua = Luba-Kasai
- pms = Piedmontese
- sco = Scots
- rue = Rusyn

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- Handle non-standard code `iw` for Hebrew used by YouTube API
- Better classification of traditional and simplified Chinese scripts
- Added basic README

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- Define constants for all file types
- fix wrong default Spanish lookup by name
- Added Sepedi and missing Tshivenda as discussed in previous PR

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- Implemented getlang_by_native_name for easier lookups