[WIP] [@nteract/web] Migrating local state to global state.

[ramantehlan]

This PR is to move the local state values to a global state(redux). It will make it easy to manage and work with the state between different components.

• Create initial global state.
• Add reducers and actions for global state values.
• Integrate global state in different components and pages.

• I have read the Contributor Guide
• I have updated the changelogs/current_changelog.md file with some information about the change that I am making the appropriate file.
• I have validated or unit-tested the changes that I have made.
• I have run through the TEST_PLAN.md to ensure that my change does not break anything else.

[lgtm-com]

This pull request fixes 3 alerts when merging 5de4f9e into bfc813f - view on LGTM.com

fixed alerts:

• 3 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 3 alerts when merging 40c6db8 into c585f42 - view on LGTM.com

fixed alerts:

• 3 for Unused variable, import, function or class

[lgtm-com]

This pull request introduces 1 alert and fixes 3 when merging 729d83a into c585f42 - view on LGTM.com

new alerts:

• 1 for Unused variable, import, function or class

fixed alerts:

• 3 for Unused variable, import, function or class

[lgtm-com]

This pull request introduces 2 alerts and fixes 7 when merging 6f003e1 into fe90b0a - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

fixed alerts:

• 6 for Unused variable, import, function or class
• 1 for Useless assignment to local variable

[lgtm-com]

This pull request introduces 2 alerts and fixes 8 when merging 383a8a2 into fe90b0a - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

fixed alerts:

• 7 for Unused variable, import, function or class
• 1 for Useless assignment to local variable

[lgtm-com]

This pull request introduces 2 alerts and fixes 8 when merging ffe5835 into 0c8e40f - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

fixed alerts:

• 7 for Unused variable, import, function or class
• 1 for Useless assignment to local variable