feat: ETC support and notifications tests

- Add ETC to the list of supported coins. A new `coin` setting can be
  configured to avoid conflict with `eth`. Mind the lowercase. By default,
  flexassitant will try to deduce the coin from the miner's address (with eth by
  default, not etc). (#5)

- Add `test` (true/false) to `notifications` section to test notifications with
  random values fetched from the Flexpool API

- Fix typo in the configuration example (#6)

BREAKING CHANGE: `notification-templates` configuration settings have been
renamed to `notifications`, with sections to configure balance, payment, block
and offline workers notifications, with `template` and `test` settings.

Signed-off-by: Julien Riou <julien@riou.xyz>

flexassistant.yaml.example

@@ -1,29 +0,0 @@
----
-database-file: flexassistant.db
-max-blocks: 10
-max-payments: 5
-miners:
-  - address: 0x0000000000000000000000000000000000000000
-    enable-balance: true
-    enable-payments: true
-    enable-offline-workers: true
-  - address: xch00000000000000000000000000000000000000000000000000000000000
-    enable-balance: true
-    enable-payments: true
-    enable-offline-workers: true
-pools:
-  - coin: eth
-    enable-blocks: true
-    min-block-reward: 10
-  - coin: xch
-    enable-blocks: true
-    min-block-reward: 1.79
-telegram:
-  chat-id: 000000000
-  channel-name: MyTelegramChannel
-  token: 0000000000000000000000000000000000000000000000
-notification-templates:
-  balance: balance.tmpl
-  block: block.tmpl
-  offline-worker; offline-worker.tmpl
-  payment: payment.tmpl