allow use of custom derivation path, and add way to increment derivation for existing

src/views/ImportAccountView.vue

@@ -24,6 +24,24 @@
       v-model="mnemonic"
     />
     {{ mnemonic }}
+    <h3
+      class="text-sm uppercase font-semibold mb-3"
+      @click="showAdvanced = !showAdvanced"
+    >
+      Advanced
+    </h3>
+    <div v-if="showAdvanced">
+      Enter a custom derivation path
+      <input
+        type="text"
+        class="block w-full rounded border border-slate-400 mb-4 px-3 py-2"
+        v-model="derivationPath"
+      />
+      For previous uPort or Endorser users,
+      <a @click="derivationPath = UPORT_DERIVATION_PATH" class="text-blue-500">
+        click here to use that value.
+      </a>
+    </div>
     <div class="mt-8">
       <button
         @click="from_mnemonic()"
@@ -44,7 +62,11 @@
 
 <script lang="ts">
 import { Component, Vue } from "vue-facing-decorator";
-import { deriveAddress, newIdentifier } from "../libs/crypto";
+import {
+  DEFAULT_ROOT_DERIVATION_PATH,
+  deriveAddress,
+  newIdentifier,
+} from "../libs/crypto";
 import { accountsDB, db } from "@/db";
 import { MASTER_SETTINGS_KEY } from "@/db/tables/settings";
 
@@ -52,11 +74,14 @@ import { MASTER_SETTINGS_KEY } from "@/db/tables/settings";
   components: {},
 })
 export default class ImportAccountView extends Vue {
+  UPORT_DERIVATION_PATH = "m/7696500'/0'/0'/0'";
+
   mnemonic = "";
   address = "";
   privateHex = "";
   publicHex = "";
-  derivationPath = "";
+  derivationPath = DEFAULT_ROOT_DERIVATION_PATH;
+  showAdvanced = false;
 
   public onCancelClick() {
     this.$router.back();
@@ -65,8 +90,10 @@ export default class ImportAccountView extends Vue {
   public async from_mnemonic() {
     const mne: string = this.mnemonic.trim().toLowerCase();
     if (this.mnemonic.trim().length > 0) {
-      [this.address, this.privateHex, this.publicHex, this.derivationPath] =
-        deriveAddress(mne);
+      [this.address, this.privateHex, this.publicHex] = deriveAddress(
+        mne,
+        this.derivationPath,
+      );
 
       const newId = newIdentifier(
         this.address,