Add demo for `ConstraintLayout` feature chaining

[hossain-khan]

Chains
Chains provide group-like behavior in a single axis (horizontally or vertically). The other axis can be constrained independently.

Creating a chain
A set of widgets are considered a chain if they are linked together via a bi-directional connection (see Fig. 9, showing a minimal chain, with two widgets).

Fig. 9 - Chain
Chain heads
Chains are controlled by attributes set on the first element of the chain (the "head" of the chain):

Fig. 10 - Chain Head
The head is the left-most widget for horizontal chains, and the top-most widget for vertical chains.

Margins in chains
If margins are specified on connections, they will be taken in account. In the case of spread chains, margins will be deducted from the allocated space.

Chain Style
When setting the attribute layout_constraintHorizontal_chainStyle or layout_constraintVertical_chainStyle on the first element of a chain, the behavior of the chain will change according to the specified style (default is CHAIN_SPREAD).

CHAIN_SPREAD -- the elements will be spread out (default style)
Weighted chain -- in CHAIN_SPREAD mode, if some widgets are set to MATCH_CONSTRAINT, they will split the available space
CHAIN_SPREAD_INSIDE -- similar, but the endpoints of the chain will not be spread out
CHAIN_PACKED -- the elements of the chain will be packed together. The horizontal or vertical bias attribute of the child will then affect the positioning of the packed elements

Fig. 11 - Chains Styles
Weighted chains
The default behavior of a chain is to spread the elements equally in the available space. If one or more elements are using MATCH_CONSTRAINT, they will use the available empty space (equally divided among themselves). The attribute layout_constraintHorizontal_weight and layout_constraintVertical_weight will control how the space will be distributed among the elements using MATCH_CONSTRAINT. For exemple, on a chain containing two elements using MATCH_CONSTRAINT, with the first element using a weight of 2 and the second a weight of 1, the space occupied by the first element will be twice that of the second element.