Fixes#190.
With this feature unsee can be configured to proxy requests to selected Alertmanager instances, if it's enabled unsee silence form will send a request via unsee rather than directly. This allows users to manage silences in environments where they have access to unsee but not to Alertmanager. Only silences endpoints on Alertmanager API are proxied.
This adds support for reading configuration from file, env support is still there and legacy env variables will still work, but flags are now following config schema, so they don't match old flags.
Having a config file allows to express more complex configuration options, which is needed for some feature requests.
This option allows for all alerts for a specified receiver, or list of
receivers, to be removed from unsee.
My use case for this is using a receiver for auto-remediation which will
contain information that the user will never need to see in the UI.
Annotations are just string maps, but to render those we need a bit more information (is it a link, should it be visible by default). Store them as more complex structs internally, this also allows us to drop alert.Links since we now have enough information to tell if annotation is a link
Strippling labels should be done after alerts are deduplicated, when user requests some alerts with a filter, not during data collection from Alertmanager. When labels are stripped before dedup then they are merged into one, because labels are needed to calculate uniqueness, which means we will return wrong data
Internal packages are supported by Go 1.5+, any package in /internal/ dir is only importable from the same repo. This will cleanup main dir a bit and provide better namespace for unsee subpackages
