[v1.18.2.r7] Firmware release

### New Features
- Esp32 touchpad functionality exposed to micropy

### Improvements
- Added RSA signature generation API to moducrypto
- Added support for saving strings in NVS - PR #226 , author: @psychogenic
- LTE class refactoring

### Bug Fix
- Fix UART.sendbreak not defaulting to 13 bits as suggested by Documentation Issue #280

Author: iwahdan88

esp32/pycom_version.h

@@ -10,7 +10,7 @@
 #ifndef VERSION_H_
 #define VERSION_H_
 
-#define SW_VERSION_NUMBER                              "1.18.2.r6"
+#define SW_VERSION_NUMBER                              "1.18.2.r7"
 
 #define LORAWAN_VERSION_NUMBER                         "1.0.2"