Fix #10954 Review button styles and remove transitions

[allyoucanmap]

Description

This PR addresses issue found after testing (see #11425 (comment)).

This PR introduces following changes:

• removal of react-transition-group and react-addons-css-transition-group, they were used but they have no effect in the user interface. This libraries were adding a span around components causing problem in particular in the toolbar. Note: most of the time transition was disabled. Also the transition of resizable modal has been removed because it has no effect on the UI
• introduction of fallback for square-button-md and square-button-md, same style as square-button
• review form-group style inside the flex-box class to ensure correct spacing
• replacement of react-spinkit inside the map plugin loader to align it with the global spinner style

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix

Issue

What is the current behavior?

#10954

What is the new behavior?

Review styles for buttons groups and removed unused transitions

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• No

Other useful information

[subashtiwari1010]

@ElenaGallo please test this fix on dev, thanks