Merge: - install: recover from error on DNS server start

Close #1293

Squashed commit of the following:

commit 0981754c5c2c67f2567ee4af0d9ab24377c53413
Merge: ef81f2c8 a6d75118
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Thu Jan 16 14:19:20 2020 +0300

    Merge remote-tracking branch 'origin/master' into 1293-install

commit ef81f2c886f3bfcff4e4352d7ecea6642be7d8e1
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Dec 30 18:32:11 2019 +0300

    linter

commit 9e205be53d9de25bd2ad63398644e14b09f95238
Author: Simon Zolin <s.zolin@adguard.com>
Date:   Mon Dec 30 17:22:17 2019 +0300

    - install: recover from error on DNS server start

    Close all modules properly
    Don't register HTTP handlers twice

dnsfilter/dnsfilter.go

@@ -577,6 +577,10 @@ func New(c *Config, filters map[int]string) *Dnsfilter {
 		}
 	}
 
+	return d
+}
+
+func (d *Dnsfilter) Start() {
 	d.filtersInitializerChan = make(chan filtersInitializerParams, 1)
 	go d.filtersInitializer()
 
@@ -584,7 +588,6 @@ func New(c *Config, filters map[int]string) *Dnsfilter {
 		d.registerSecurityHandlers()
 		d.registerRewritesHandlers()
 	}
-	return d
 }
 
 //