App Setup + Managing default settings

[pedrorezende]

This PR contains a few improvements on how Namadillo manages the app settings. These new features are listed below:

• App now displays some useful error messages depending on the type of error experienced by the user
• If Namadillo is being set up without any indexer or prior config, a new indexer settings screen will appear
• Introduces a new config.toml file on /public folder, where you can set up a default config for the installation
• Adds an atom to verify if the indexer url is valid
• Refactors page loader

[github-actions[bot]]

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