Migrate to SQLCipher for messages/cache

Quite a few other fixes, including:
  - Sending to contact with no avatar yet (not synced from mobile)
  - Left pane doesn't update quickly or at all on new message
  - Left pane doesn't show sent or error status

Also:
 - Contributing.md: Ensure set of linux dev dependencies is complete

app/sql_channel.js

@@ -0,0 +1,55 @@
+const electron = require('electron');
+const sql = require('./sql');
+
+const { ipcMain } = electron;
+
+module.exports = {
+  initialize,
+};
+
+let initialized = false;
+
+const SQL_CHANNEL_KEY = 'sql-channel';
+const ERASE_SQL_KEY = 'erase-sql-key';
+
+function initialize({ userConfig }) {
+  if (initialized) {
+    throw new Error('sqlChannels: already initialized!');
+  }
+  initialized = true;
+
+  if (!userConfig) {
+    throw new Error('initialize: userConfig is required!');
+  }
+
+  ipcMain.on(SQL_CHANNEL_KEY, async (event, jobId, callName, ...args) => {
+    try {
+      const fn = sql[callName];
+      if (!fn) {
+        throw new Error(
+          `sql channel: ${callName} is not an available function`
+        );
+      }
+
+      const result = await fn(...args);
+      event.sender.send(`${SQL_CHANNEL_KEY}-done`, jobId, null, result);
+    } catch (error) {
+      const errorForDisplay = error && error.stack ? error.stack : error;
+      console.log(
+        `sql channel error with call ${callName}: ${errorForDisplay}`
+      );
+      event.sender.send(`${SQL_CHANNEL_KEY}-done`, jobId, errorForDisplay);
+    }
+  });
+
+  ipcMain.on(ERASE_SQL_KEY, async event => {
+    try {
+      userConfig.set('key', null);
+      event.sender.send(`${ERASE_SQL_KEY}-done`);
+    } catch (error) {
+      const errorForDisplay = error && error.stack ? error.stack : error;
+      console.log(`sql-erase error: ${errorForDisplay}`);
+      event.sender.send(`${ERASE_SQL_KEY}-done`, error);
+    }
+  });
+}