Fix for #665 and additional fix for #663.

If your segemnts are broken or Mailtrain complains about missing 20190726150000_shorten_field_column_names.js, run the following in `server/setup/knex/fixes`:

```NODE_ENV=production node fix-20190726150000_shorten_field_column_names.js```

server/setup/knex/fixes/fix-20190726150000_shorten_field_column_names.js

@@ -0,0 +1,69 @@
+'use strict';
+
+const config = require('../config');
+const knex = require('../../../lib/knex');
+const shortid = require('shortid');
+const slugify = require('slugify');
+
+async function run() {
+    const lists = await knex('lists');
+    for (const list of lists) {
+        console.log(`Processing list ${list.id}`);
+        const fields = await knex('custom_fields').whereNotNull('column').where('list', list.id);
+
+        const fieldsMap = new Map();
+        const prefixesMap = new Map();
+
+        for (const field of fields) {
+            const oldName = field.column;
+            const newName = ('custom_' + slugify(field.name, '_').substring(0, 32) + '_' + shortid.generate()).toLowerCase().replace(/[^a-z0-9_]/g, '_');
+            const formerPrefix = ('custom_' + slugify(field.name, '_') + '_').toLowerCase().replace(/[^a-z0-9_]/g, '');
+
+            fieldsMap.set(oldName, newName);
+            prefixesMap.set(formerPrefix, newName);
+
+            await knex('custom_fields').where('id', field.id).update('column', newName);
+
+            await knex.schema.table('subscription__' + list.id, table => {
+                table.renameColumn(oldName, newName);
+                table.renameColumn('source_' + oldName, 'source_' + newName);
+            });
+        }
+
+
+        function processRule(rule) {
+            if (rule.type === 'all' || rule.type === 'some' || rule.type === 'none') {
+                for (const childRule of rule.rules) {
+                    processRule(childRule);
+                }
+            } else {
+                let newName = fieldsMap.get(rule.column);
+                if (newName) {
+                    rule.column = newName;
+                    return;
+                }
+
+                for (const [formerPrefix, newName] of prefixesMap.entries()) {
+                    if (rule.column.startsWith(formerPrefix)) {
+                        rule.column = newName;
+                        return;
+                    }
+                }
+            }
+        }
+
+        const segments = await knex('segments').where('list', list.id);
+        for (const segment of segments) {
+            const settings = JSON.parse(segment.settings);
+            processRule(settings.rootRule);
+            await knex('segments').where('id', segment.id).update({settings: JSON.stringify(settings)});
+        }
+    }
+
+    await knex('knex_migrations').where('name', '20190726150000_shorten_field_column_names.js').del();
+
+    console.log('All fixes done');
+    process.exit();
+}
+
+run().catch(err => console.error(err));