Refactor Loadpage UI & Server to Read First 100 Rows Upon Upload

[tonywu1999]

Story

Right now, users will click the browse button to upload a dataset into a temp folder, and then when they click Upload data, MSstatsShiny will read the dataset into RAM.

The ideal user story is if the user clicks the browse button that provides a filepath to their dataset (whether that filepath is corresponding to a tmp filepath or a local filepath), and then MSstatsShiny reads the first 100 rows the dataset to dynamically update the fields / settings.

Subtasks

• Refactor Loadpage UI & Server to read the first 100 rows of the dataset into RAM upon clicking and uploading a dataset via the browse button
• For the Metamorpheus PTM converter, provide a dropdown of the possible modifications that can be used (rather than the user providing the string)
  • And add Other in case the first 100 rows don't cover what the user is looking for.