Refac visualisation module

[ntorresd]

This PR:

• closes #136
• closes #129
• Allows for data binning in seroprevalence plots
• Changes age grouping behavior - Intervals are now open to the left and closed to the right (denoted as (a,b])
• Sets automatic xlim/ylim in seroprevalence plots
• Set both Bayesian credible intervals and frequentist confidence interval using single parameter alpha (set as default to 0.05)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.58768% with 176 lines in your changes are missing coverage. Please review.

Project coverage is 69.89%. Comparing base (cd95652) to head (97b57e3). Report is 1 commits behind head on main.

:exclamation: Current head 97b57e3 differs from pull request most recent head 7882d71. Consider uploading reports for the commit 7882d71 to get more accurate results

Files	Patch %	Lines
R/visualisation.R	0.00%	144 Missing :warning:
R/seroprevalence_data.R	43.47%	26 Missing :warning:
R/modelling.R	71.42%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #162 +/- ## ========================================== + Coverage 68.59% 69.89% +1.29% ========================================== Files 10 10 Lines 1777 1744 -33 ========================================== Hits 1219 1219 + Misses 558 525 -33 ```

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