Add function for loading raw files from MetaboLights

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 43 lines in your changes missing coverage. Please review.

Project coverage is 15.18%. Comparing base (7e58ebf) to head (43e6c8a). Report is 9 commits behind head on devel.

Files with missing lines	Patch %	Lines
R/getMetaboLights.R	0.00%	43 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #31 +/- ## ========================================== - Coverage 15.82% 15.18% -0.64% ========================================== Files 5 5 Lines 714 744 +30 ========================================== Hits 113 113 - Misses 601 631 +30 ``` | [Flag](https://app.codecov.io/gh/EBI-Metagenomics/HoloFoodR/pull/31/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EBI-Metagenomics) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/EBI-Metagenomics/HoloFoodR/pull/31/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EBI-Metagenomics) | `15.18% <0.00%> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EBI-Metagenomics#carryforward-flags-in-the-pull-request-comment) to find out more.

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