split `push` to `push` and `pushAll` (and related changes)

[stepancheg]

Split 'push' and 'pushAll', 'insert' and 'insertAll', 'pushFront' and 'pushFrontAll'.

Basically,

'xxx' adds single element to sequence 'xxxAll' adds sequence elements

This separation makes:

• simpler overload resolution
• simpler push and other function implementations
• client code easier to read

"All" suffix is chosen after Java collections API (List has add, addAll methods). Suggestions of better function names are welcome.