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>

utils.go

@@ -14,6 +14,8 @@ const MojoToXCHDivider = 1000000000000
 // Example: for "eth", convert from Weis to ETH
 func ConvertCurrency(coin string, value float64) (float64, error) {
 	switch coin {
+	case "etc":
+		return ConvertWeis(value), nil
 	case "eth":
 		return ConvertWeis(value), nil
 	case "xch":
@@ -36,6 +38,8 @@ func ConvertMojo(value float64) float64 {
 // FormatBlockURL returns the URL on the respective blockchain explorer given the coin and the block hash
 func FormatBlockURL(coin string, hash string) (string, error) {
 	switch coin {
+	case "etc":
+		return fmt.Sprintf("https://etcblockexplorer.com/block/%s", hash), nil
 	case "eth":
 		return fmt.Sprintf("https://etherscan.io/block/%s", hash), nil
 	case "xch":
@@ -47,6 +51,8 @@ func FormatBlockURL(coin string, hash string) (string, error) {
 // FormatTransactionURL returns the URL on the respective blockchain explorer given the coin and the transaction hash
 func FormatTransactionURL(coin string, hash string) (string, error) {
 	switch coin {
+	case "etc":
+		return fmt.Sprintf("https://etcblockexplorer.com/address/%s", hash), nil
 	case "eth":
 		return fmt.Sprintf("https://etherscan.io/tx/%s", hash), nil
 	case "xch":