Decimal point support for all readings

[emartynov]

It is changes for #364.

I'm sorry but I also did small improvements in code that are not related to the required change.

Changes:

1. Updated Realm to newest version
2. Added migration for all readings and user max and min settings
3. Updated code to make things compilable
4. Updated UI to enable entering the double values

Not required changes:

1. Migrated to API 26
2. Removed some duplicated code and simplified some tests

[coveralls]

Coverage increased (+1.5%) to 17.998% when pulling f47a02c4f90e1d241c68753afb112b3e15d9398e on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+1.5%) to 17.998% when pulling f47a02c4f90e1d241c68753afb112b3e15d9398e on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+1.5%) to 17.998% when pulling 78d7382ee0308c5a56640a4113b9bcc011f63e08 on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+1.6%) to 18.077% when pulling fbd320c89a7d7633c7862ddaee077a1536c62e83 on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+1.5%) to 18.066% when pulling 5a5a26b595ed81a96084963fcf24f870b49ffa3c on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+1.6%) to 18.118% when pulling 3766d27fd15ca3fafc14d8f9ad3ce2758a90c3cb on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+1.6%) to 18.122% when pulling ad2a9644d096e3dba6dbd6f55dc1c3a23b136611 on decimal-point into 2b9a433919de71e716604dd6082abf8bf1542b42 on develop.

[coveralls]

Coverage increased (+2.5%) to 19.154% when pulling 411a6d2e4f119d7020ccc659e273601d1cf98fd3 on decimal-point into 932e9b0985f61d9c1fb89db7f5436bf36eda2252 on develop.