[#977] Replace user-facing Secant with Zashi

- All in-app strings were changed some time back. This PR changes repository documentation occurrences.
- Closes #977

.github/ISSUE_TEMPLATE/bug-report.md

@@ -1,6 +1,6 @@
 ---
 name: Bug report
-about: Create a report about a bug in Secant Android Wallet.
+about: Create a report about a bug in Zashi Android Wallet.
 title: ''
 labels: 'bug'
 assignees: ''
@@ -8,7 +8,7 @@ assignees: ''
 ---
 
 <!--
-This issue tracker is only for technical issues related to Secant Android Wallet.
+This issue tracker is only for technical issues related to Zashi Android Wallet.
 
 General Zcash questions and/or support requests and are best directed to either:
  * Zcash Forum: https://forum.zcashcommunity.com/)

.github/ISSUE_TEMPLATE/feature-request.md

@@ -1,6 +1,6 @@
 ---
 name: Feature request
-about: Suggest an idea for the Secant wallet.
+about: Suggest an idea for the Zashi wallet.
 title: ''
 labels: 'use case'
 assignees: ''

README.md

@@ -1,4 +1,4 @@
-# Secant Android Wallet
+# Zashi Android Wallet
 This is a sample implementation of a Zcash wallet for Android leveraging the [Zcash Android SDK](https://github.com/zcash/zcash-android-wallet-sdk).  The goal is to exercise the SDK and related Zcash libraries, as well as demonstrate how the SDK works.
 
 While we aim to continue improving this sample, it is not an official product.  We open sourced it as a resource to make wallet development easier for the Zcash ecosystem.