The change introduces new entity `manager` which replaces
`watchdog`, decouples requestHandler and groups. Manager
supposed to control life cycle of groups, rules and
config reloads.
Groups export an ID method which returns a hash
from filename and group name. ID supposed to be unique
identifier across all loaded groups.
Some tests were added to improve coverage.
Bug with wrong annotation value if $value is used in
templates after metrics being restored fixed.
Notifier interface was extended to accept context.
New set of metrics was introduced for config reload.
* app/vmalert: initial remote-write support for alerts state persistence.
If `remotewrite.url` flag is set, vmalert will send alerts state via remote-write protocol to remote storage. The sending is asynchronous to avoid blocking calls in rules evaluation loop.
* app/vmalert: merge with master
* app/vmalert: write both `instant` and `for` alerts timeseries states in remote storage.
* Initial rules evaluation support.
Rules are now store alerts state in private field `alerts`. Every evaluation updates
the alerts and state. Every unique metric received from datastore represents a unique alert,
uniqueness is guaranteed by hashing ordered labelset.
* merge with master
* cleanup
* support endAt parameter as 3*evaluationInterval for active alerts
* make golint happy
