Move configs into “BaGet” section

[loic-sharma]

Is your feature request related to a problem? Please describe.

You should be able to embed BaGet into an existing web app without clobbering options. Currently BaGet has config keys like Database and Storage that are likely to conflict with other web apps' configs.

Describe the solution you'd like

BaGet's configs should be nested in a section. For example:

{
  "BaGet": {
    "Database": { ... },
    "Storage": { ... }
  }
}