Add translation strings and placeholders for config fields

[rudokemper]

Closes #69.

Goal

To improve the config form field labels and placeholders on the front end.

Screenshots

Before	After

What I changed

• Introduced and applied toCamelCase function to utils to transform KEY_TEXT to keyText across label fields for all config components.
• Added translations for each (camel-cased) form field.
• Added placeholders for some of the fields where useful (such as Mapbox access token and style).
• Turned FILTER_OUT_VALUES_FROM_COLUMN into a tag field.