"E" character appears when copy special -> copy insert statement

## What did you do?
Copy and paste the insert statement from the contextual menu "Copy Insert Statement"

## What did you expect to happen?

I paste the source code to the editor, and the "E" char appears.

```
INSERT INTO "public"."mall_settings"("mall_setting_references_key","mall_id","value")
VALUES
(E'receipt_date_subtitle',E'0UBtU-Qs',E'Loyalty System'),
(E'redeem_format',E'0UBtU-Qs',E'RED-{timestamp}-{code}-{username}'),
(E'redeemevoucher_prefix',E'0UBtU-Qs',E'CRM-EV');
```

## What software versions are you using?

Postico version:
(select "About Postico" from the Postico menu)

macOS version:
10.13.2

PostgreSQL version:
PostgreSQL 9.5.4 on x86_64-apple-darwin16.0.0, compiled by Apple LLVM version 8.0.0 (clang-800.0.38), 64-bit

Postico 1.2.3

Thank you.

No source file or test is named. Start by reproducing the contextual-menu “Copy Insert Statement” action with the reported PostgreSQL and Postico versions, then inspect the code path that generates the copied SQL. Done means the pasted INSERT statement no longer contains unexpected E prefixes and the behavior is covered by a regression test.

Written by the indexing model from the issue text.