feat(grid): Added mixin for push and pull elements

-- rename _columns.scss to _grid.scss
-- added tests with new classes for push and pull
refactor(svg): different file-formats are possbile

-- variable for file-format
-- added example
chore(tests): correct path to components
refactor(grunt): watch each application.scss in tests-folder
chore(documentation): docu for placeholder, svg-fallback and user-select
feat(completions): user-select as mixin for cross-browser-functionality
Merge branch 'master' of github.com:timhartmann/scss-components
Merge pull request #2 from timhartmann/svg-fallback

refactor(svg): different file-formats are possible
Merge pull request #3 from timhartmann/grid-helpers

feat(grid): Added mixin for push and pull elements
chore(documentation): docu for grid-helpers like push and pull
Update README.md
Update README.md