e2e search tokens

[dennis00010011b]

Relates to #135

Added e2e tests for Add token: search feature:

      add Mainnet's tokens
        ✓ field 'Search' is displayed (3054ms)
        ✓ button 'Next' is disabled if no tokens found (171ms)
        ✓ button 'Cancel' is enabled and lead to main screen  (187ms)
        ✓ Search by name: searching result list is empty if request invalid (2601ms)
        ✓ Search by name: searching result list isn't empty  (1177ms)
        ✓ Token's info contains name, symbol and picture 
        ✓ button 'Next' is disabled if no one token is selected (131ms)
        ✓ user can select one token (180ms)
        ✓ button 'Next' is enabled if token is selected (137ms)
        ✓ user can unselected token (165ms)
        ✓ button 'Next' is disabled after token was unselected (132ms)
        ✓ user can select two tokens (247ms)
        ✓ click button 'Next' opens confirm screen  (360ms)
        ✓ two selected tokens displayed and have correct parameters (2139ms)
        ✓ button 'Cancel' is enabled and leads to main screen  (353ms)
        ✓ button 'Next' is enabled if confirmation list isn't empty (467ms)
        ✓ Search by contract address: searching result list is empty if address invalid  (2876ms)
        ✓ Search by valid contract address: searching result list contains one token  (2527ms)
        ✓ Token's info contains correct name  (159ms)
        ✓ one more token added to confirmation list (334ms)
        ✓ button 'Add tokens' is enabled and clickable (326ms)
        ✓ all selected tokens are displayed on main screen (153ms)
        ✓ correct value of counter of owned tokens (162ms)
      Token should be displayed only for network, where it was added 
        ✓ token should not  be displayed in POA network (1641ms)
        ✓ token should not  be displayed in SOKOL network (1612ms)
        - token should not  be displayed in LOCALHOST network
        ✓ token should not  be displayed in ROPSTEN network (1589ms)
        ✓ token should not  be displayed in KOVAN network (1601ms)
        ✓ token should not  be displayed in RINKEBY network (1574ms)
      remove Mainnet's tokens
        ✓ remove tokens (3428ms)