- Added to main menu possibility to export and import all application date.

- Improved encryption/decryption of exported/imported data.  If accounts
  were exported, they need to be exported again.
- Lots of other implemetation improvements.

app/src/main/kotlin/com/tutpro/baresip/Contact.kt

@@ -1,5 +1,6 @@
 package com.tutpro.baresip
 
+import java.nio.charset.StandardCharsets
 import java.util.ArrayList
 
 class Contact(var name: String, var uri: String) {
@@ -12,5 +13,47 @@ class Contact(var name: String, var uri: String) {
             return BaresipService.contacts
         }
 
+        fun save(): Boolean {
+            var contents = ""
+            for (c in BaresipService.contacts) contents += "\"${c.name}\" <${c.uri}>\n"
+            return Utils.putFileContents(BaresipService.filesPath + "/contacts",
+                    contents.toByteArray())
+        }
+
+        fun restore(): Boolean {
+            val content = Utils.getFileContents(BaresipService.filesPath + "/contacts")
+            if (content == null) return false
+            val contacts = String(content, StandardCharsets.ISO_8859_1)
+            Api.contacts_remove()
+            BaresipService.contacts.clear()
+            contacts.lines().forEach {
+                val parts = it.split("\"")
+                if (parts.size == 3) {
+                    val name = parts[1]
+                    var uri = parts[2].trim()
+                    if (uri.startsWith("<"))
+                        uri = uri.substringAfter("<").substringBefore(">")
+                    // Currently no need to make baresip aware of the contact
+                    // Api.contact_add("\"$name\" $uri")
+                    BaresipService.contacts.add(Contact(name, uri))
+                }
+            }
+            return true
+        }
+
+        fun export(): Boolean {
+            return Utils.putFileContents(BaresipService.downloadsPath + "/contacts.bs",
+                    Utils.getFileContents(BaresipService.filesPath + "/contacts")!!)
+        }
+
+        fun import(): Boolean {
+            val contacts = Utils.getFileContents(BaresipService.downloadsPath + "/contacts.bs")
+            if (contacts != null) {
+                Utils.putFileContents(BaresipService.filesPath + "/contacts", contacts)
+                return restore()
+            }
+            return false
+        }
+
     }
 }