Add two nodes for substring

[daniil-loban]

Features for text:

substring_by_index node that allows extract a sub-string from String Value for example:

• in String Value: "a;b;c" (from a csv file or a http request)
• param delimeter: ";"
• param index: 1
• out: "b"

count_substring node just count specified sub-string (useful for check max Index in substring_by_index) example:

• in String Value: "a;b;c";
• param substring: ";"
• out: 2 (if substring "" out is 0)